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 $210.77   10.642%   $233.2001   $233.20   $233.20   $233.20  
  Purchase #2 $14.90   10.324%   $16.4383   $16.44   $16.45   $16.40  
  Purchase #3 $236.90   11.667%   $264.5391   $264.54   $264.55   $264.50  
  Purchase #4 $54.31   7.823%   $58.5587   $58.56   $58.55   $58.60  
  Purchase #5 $125.80   7.796%   $135.6074   $135.61   $135.60   $135.60  
  Purchase #6 $100.75   11.326%   $112.1609   $112.16   $112.15   $112.20  
  Purchase #7 $225.49   10.198%   $248.4855   $248.49   $248.50   $248.50  
  7 purchase totals = $968.92       $1,068.9900   $1,069.00   $1,069.00   $1,069.00