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 $141.58   9.219%   $154.6323   $154.63   $154.65   $154.60  
  Purchase #2 $191.56   13.821%   $218.0355   $218.04   $218.05   $218.00  
  Purchase #3 $131.69   11.307%   $146.5802   $146.58   $146.60   $146.60  
  Purchase #4 $68.26   4.327%   $71.2136   $71.21   $71.20   $71.20  
  Purchase #5 $109.42   9.618%   $119.944   $119.94   $119.95   $119.90  
  Purchase #6 $60.55   11.412%   $67.46   $67.46   $67.45   $67.50  
  Purchase #7 $61.31   4.398%   $64.0064   $64.01   $64.00   $64.00  
  7 purchase totals = $764.37       $841.8720   $841.87   $841.90   $841.80