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 $217.33   12.654%   $244.8309   $244.83   $244.85   $244.80  
  Purchase #2 $89.93   9.337%   $98.3268   $98.33   $98.35   $98.30  
  Purchase #3 $215.95   12.802%   $243.5959   $243.60   $243.60   $243.60  
  Purchase #4 $204.65   12.282%   $229.7851   $229.79   $229.80   $229.80  
  Purchase #5 $73.26   3.231%   $75.627   $75.63   $75.65   $75.60  
  Purchase #6 $28.58   13.804%   $32.5252   $32.53   $32.55   $32.50  
  Purchase #7 $148.79   8.663%   $161.6797   $161.68   $161.70   $161.70  
  7 purchase totals = $978.49       $1,086.3706   $1,086.39   $1,086.50   $1,086.30