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 $68.41   11.592%   $76.3401   $76.34   $76.35   $76.30  
  Purchase #2 $77.28   9.243%   $84.423   $84.42   $84.40   $84.40  
  Purchase #3 $38.52   4.676%   $40.3212   $40.32   $40.30   $40.30  
  Purchase #4 $230.64   4.629%   $241.3163   $241.32   $241.30   $241.30  
  Purchase #5 $93.73   9.149%   $102.3054   $102.31   $102.30   $102.30  
  Purchase #6 $180.94   11.656%   $202.0304   $202.03   $202.05   $202.00  
  Purchase #7 $174.67   7.714%   $188.144   $188.14   $188.15   $188.10  
  7 purchase totals = $864.19       $934.8804   $934.88   $934.85   $934.70