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 $128.70   8.856%   $140.0977   $140.10   $140.10   $140.10  
  Purchase #2 $210.71   13.142%   $238.4015   $238.40   $238.40   $238.40  
  Purchase #3 $166.96   9.827%   $183.3672   $183.37   $183.35   $183.40  
  Purchase #4 $16.58   5.536%   $17.4979   $17.50   $17.50   $17.50  
  Purchase #5 $120.70   8.693%   $131.1925   $131.19   $131.20   $131.20  
  Purchase #6 $112.29   10.136%   $123.6717   $123.67   $123.65   $123.70  
  Purchase #7 $40.48   11.805%   $45.2587   $45.26   $45.25   $45.30  
  7 purchase totals = $796.42       $879.4872   $879.49   $879.45   $879.60