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 $134.82   5.227%   $141.867   $141.87   $141.85   $141.90  
  Purchase #2 $122.56   10.413%   $135.3222   $135.32   $135.30   $135.30  
  Purchase #3 $140.59   10.851%   $155.8454   $155.85   $155.85   $155.80  
  Purchase #4 $246.44   12.556%   $277.383   $277.38   $277.40   $277.40  
  Purchase #5 $184.79   5.594%   $195.1272   $195.13   $195.15   $195.10  
  Purchase #6 $20.81   6.748%   $22.2143   $22.21   $22.20   $22.20  
  Purchase #7 $26.82   4.278%   $27.9674   $27.97   $27.95   $28.00  
  7 purchase totals = $876.83       $955.7265   $955.73   $955.70   $955.70