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 $55.49   11.401%   $61.8164   $61.82   $61.80   $61.80  
  Purchase #2 $87.94   12.183%   $98.6537   $98.65   $98.65   $98.70  
  Purchase #3 $102.51   13.444%   $116.2914   $116.29   $116.30   $116.30  
  Purchase #4 $72.60   4.788%   $76.0761   $76.08   $76.10   $76.10  
  Purchase #5 $196.30   10.570%   $217.0489   $217.05   $217.05   $217.00  
  Purchase #6 $224.82   11.323%   $250.2764   $250.28   $250.30   $250.30  
  Purchase #7 $65.96   12.136%   $73.9649   $73.96   $73.95   $74.00  
  7 purchase totals = $805.62       $894.1278   $894.13   $894.15   $894.20