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 $68.85   11.181%   $76.5481   $76.55   $76.55   $76.50  
  Purchase #2 $117.96   13.829%   $134.2727   $134.27   $134.25   $134.30  
  Purchase #3 $6.90   13.780%   $7.8508   $7.85   $7.85   $7.90  
  Purchase #4 $160.46   4.218%   $167.2282   $167.23   $167.25   $167.20  
  Purchase #5 $190.61   11.193%   $211.945   $211.95   $211.95   $211.90  
  Purchase #6 $243.56   5.481%   $256.9095   $256.91   $256.90   $256.90  
  Purchase #7 $7.79   6.581%   $8.3027   $8.30   $8.30   $8.30  
  7 purchase totals = $796.13       $863.0570   $863.06   $863.05   $863.00