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 $85.37   9.208%   $93.2309   $93.23   $93.25   $93.20  
  Purchase #2 $102.66   4.801%   $107.5887   $107.59   $107.60   $107.60  
  Purchase #3 $150.80   3.526%   $156.1172   $156.12   $156.10   $156.10  
  Purchase #4 $168.93   12.773%   $190.5074   $190.51   $190.50   $190.50  
  Purchase #5 $114.56   6.818%   $122.3707   $122.37   $122.35   $122.40  
  Purchase #6 $246.89   10.145%   $271.937   $271.94   $271.95   $271.90  
  Purchase #7 $63.92   7.257%   $68.5587   $68.56   $68.55   $68.60  
  7 purchase totals = $933.13       $1,010.3106   $1,010.32   $1,010.30   $1,010.30