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 $235.34   13.571%   $267.278   $267.28   $267.30   $267.30  
  Purchase #2 $144.96   8.258%   $156.9308   $156.93   $156.95   $156.90  
  Purchase #3 $161.54   5.289%   $170.0839   $170.08   $170.10   $170.10  
  Purchase #4 $102.92   8.368%   $111.5323   $111.53   $111.55   $111.50  
  Purchase #5 $101.92   4.607%   $106.6155   $106.62   $106.60   $106.60  
  Purchase #6 $184.72   13.348%   $209.3764   $209.38   $209.40   $209.40  
  Purchase #7 $155.55   11.800%   $173.9049   $173.90   $173.90   $173.90  
  7 purchase totals = $1,086.95       $1,195.7218   $1,195.72   $1,195.80   $1,195.70