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 $80.45   3.119%   $82.9592   $82.96   $82.95   $83.00  
  Purchase #2 $153.71   4.107%   $160.0229   $160.02   $160.00   $160.00  
  Purchase #3 $157.70   13.873%   $179.5777   $179.58   $179.60   $179.60  
  Purchase #4 $98.61   8.872%   $107.3587   $107.36   $107.35   $107.40  
  Purchase #5 $200.84   12.229%   $225.4007   $225.40   $225.40   $225.40  
  Purchase #6 $144.47   6.237%   $153.4806   $153.48   $153.50   $153.50  
  Purchase #7 $53.49   6.829%   $57.1428   $57.14   $57.15   $57.10  
  7 purchase totals = $889.27       $965.9426   $965.94   $965.95   $966.00