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 $63.57   6.611%   $67.7726   $67.77   $67.75   $67.80  
  Purchase #2 $90.70   7.262%   $97.2866   $97.29   $97.30   $97.30  
  Purchase #3 $249.77   7.131%   $267.5811   $267.58   $267.60   $267.60  
  Purchase #4 $152.33   7.290%   $163.4349   $163.43   $163.45   $163.40  
  Purchase #5 $102.56   5.855%   $108.5649   $108.56   $108.55   $108.60  
  Purchase #6 $214.68   12.113%   $240.6842   $240.68   $240.70   $240.70  
  Purchase #7 $37.68   9.661%   $41.3203   $41.32   $41.30   $41.30  
  7 purchase totals = $911.29       $986.6446   $986.63   $986.65   $986.70