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 $153.74   8.635%   $167.0154   $167.02   $167.00   $167.00  
  Purchase #2 $193.54   5.198%   $203.6002   $203.60   $203.60   $203.60  
  Purchase #3 $211.54   12.125%   $237.1892   $237.19   $237.20   $237.20  
  Purchase #4 $98.75   5.431%   $104.1131   $104.11   $104.10   $104.10  
  Purchase #5 $145.77   13.362%   $165.2478   $165.25   $165.25   $165.20  
  Purchase #6 $185.39   12.537%   $208.6323   $208.63   $208.65   $208.60  
  Purchase #7 $70.71   13.865%   $80.5139   $80.51   $80.50   $80.50  
  7 purchase totals = $1,059.44       $1,166.3119   $1,166.31   $1,166.30   $1,166.20