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 $58.73   10.284%   $64.7698   $64.77   $64.75   $64.80  
  Purchase #2 $38.79   13.759%   $44.1271   $44.13   $44.15   $44.10  
  Purchase #3 $218.31   6.249%   $231.9522   $231.95   $231.95   $232.00  
  Purchase #4 $186.56   13.570%   $211.8762   $211.88   $211.90   $211.90  
  Purchase #5 $65.37   4.798%   $68.5065   $68.51   $68.50   $68.50  
  Purchase #6 $44.37   4.297%   $46.2766   $46.28   $46.30   $46.30  
  Purchase #7 $50.31   11.197%   $55.9432   $55.94   $55.95   $55.90  
  7 purchase totals = $662.44       $723.4516   $723.46   $723.50   $723.50