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 $245.42   7.239%   $263.186   $263.19   $263.20   $263.20  
  Purchase #2 $217.52   4.342%   $226.9647   $226.96   $226.95   $227.00  
  Purchase #3 $211.71   10.355%   $233.6326   $233.63   $233.65   $233.60  
  Purchase #4 $55.76   11.229%   $62.0213   $62.02   $62.00   $62.00  
  Purchase #5 $100.60   9.289%   $109.9447   $109.94   $109.95   $109.90  
  Purchase #6 $38.36   6.808%   $40.9715   $40.97   $40.95   $41.00  
  Purchase #7 $126.95   11.697%   $141.7993   $141.80   $141.80   $141.80  
  7 purchase totals = $996.32       $1,078.5201   $1,078.51   $1,078.50   $1,078.50