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 $112.78   4.565%   $117.9284   $117.93   $117.95   $117.90  
  Purchase #2 $148.64   12.118%   $166.6522   $166.65   $166.65   $166.70  
  Purchase #3 $102.81   7.131%   $110.1414   $110.14   $110.15   $110.10  
  Purchase #4 $201.41   7.411%   $216.3365   $216.34   $216.35   $216.30  
  Purchase #5 $197.29   10.145%   $217.3051   $217.31   $217.30   $217.30  
  Purchase #6 $118.85   4.808%   $124.5643   $124.56   $124.55   $124.60  
  Purchase #7 $55.73   9.497%   $61.0227   $61.02   $61.00   $61.00  
  7 purchase totals = $937.51       $1,013.9506   $1,013.95   $1,013.95   $1,013.90