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 $84.53   11.141%   $93.9475   $93.95   $93.95   $93.90  
  Purchase #2 $34.61   13.830%   $39.3966   $39.40   $39.40   $39.40  
  Purchase #3 $138.41   10.256%   $152.6053   $152.61   $152.60   $152.60  
  Purchase #4 $242.38   4.629%   $253.5998   $253.60   $253.60   $253.60  
  Purchase #5 $221.38   9.794%   $243.062   $243.06   $243.05   $243.10  
  Purchase #6 $172.37   6.323%   $183.269   $183.27   $183.25   $183.30  
  Purchase #7 $168.33   5.536%   $177.6487   $177.65   $177.65   $177.60  
  7 purchase totals = $1,062.01       $1,143.5289   $1,143.54   $1,143.50   $1,143.50