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 $43.83   10.208%   $48.3042   $48.30   $48.30   $48.30  
  Purchase #2 $216.43   7.522%   $232.7099   $232.71   $232.70   $232.70  
  Purchase #3 $123.50   13.677%   $140.3911   $140.39   $140.40   $140.40  
  Purchase #4 $218.88   4.591%   $228.9288   $228.93   $228.95   $228.90  
  Purchase #5 $210.52   5.621%   $222.3533   $222.35   $222.35   $222.40  
  Purchase #6 $124.79   11.474%   $139.1084   $139.11   $139.10   $139.10  
  Purchase #7 $36.58   10.182%   $40.3046   $40.30   $40.30   $40.30  
  7 purchase totals = $974.53       $1,052.1003   $1,052.09   $1,052.10   $1,052.10