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 $111.76   13.825%   $127.2108   $127.21   $127.20   $127.20  
  Purchase #2 $205.79   13.667%   $233.9153   $233.92   $233.90   $233.90  
  Purchase #3 $173.84   11.659%   $194.108   $194.11   $194.10   $194.10  
  Purchase #4 $127.56   8.650%   $138.5939   $138.59   $138.60   $138.60  
  Purchase #5 $9.94   10.369%   $10.9707   $10.97   $10.95   $11.00  
  Purchase #6 $147.64   12.667%   $166.3416   $166.34   $166.35   $166.30  
  Purchase #7 $70.85   6.248%   $75.2767   $75.28   $75.30   $75.30  
  7 purchase totals = $847.38       $946.4170   $946.42   $946.40   $946.40