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 $88.35   3.871%   $91.77   $91.77   $91.75   $91.80  
  Purchase #2 $155.49   8.714%   $169.0394   $169.04   $169.05   $169.00  
  Purchase #3 $229.53   11.306%   $255.4807   $255.48   $255.50   $255.50  
  Purchase #4 $212.69   12.252%   $238.7488   $238.75   $238.75   $238.70  
  Purchase #5 $76.85   11.139%   $85.4103   $85.41   $85.40   $85.40  
  Purchase #6 $165.70   11.690%   $185.0703   $185.07   $185.05   $185.10  
  Purchase #7 $178.54   13.816%   $203.2071   $203.21   $203.20   $203.20  
  7 purchase totals = $1,107.15       $1,228.7266   $1,228.73   $1,228.70   $1,228.70