Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $153.32   8.349%   $166.1207   $166.12   $166.10   $166.10  
  Purchase #2 $241.58   9.356%   $264.1822   $264.18   $264.20   $264.20  
  Purchase #3 $148.31   11.785%   $165.7883   $165.79   $165.80   $165.80  
  Purchase #4 $185.60   12.226%   $208.2915   $208.29   $208.30   $208.30  
  Purchase #5 $109.47   8.725%   $119.0213   $119.02   $119.00   $119.00  
  Purchase #6 $149.49   10.622%   $165.3688   $165.37   $165.35   $165.40  
  Purchase #7 $102.35   10.256%   $112.847   $112.85   $112.85   $112.80  
  7 purchase totals = $1,090.12       $1,201.6198   $1,201.62   $1,201.60   $1,201.60