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 $228.25   10.843%   $252.9991   $253.00   $253.00   $253.00  
  Purchase #2 $171.36   5.221%   $180.3067   $180.31   $180.30   $180.30  
  Purchase #3 $129.90   5.443%   $136.9705   $136.97   $136.95   $137.00  
  Purchase #4 $238.78   12.449%   $268.5057   $268.51   $268.50   $268.50  
  Purchase #5 $182.60   13.789%   $207.7787   $207.78   $207.80   $207.80  
  Purchase #6 $39.35   12.375%   $44.2196   $44.22   $44.20   $44.20  
  Purchase #7 $237.30   7.821%   $255.8592   $255.86   $255.85   $255.90  
  7 purchase totals = $1,227.54       $1,346.6395   $1,346.65   $1,346.60   $1,346.70