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 $67.28   13.381%   $76.2827   $76.28   $76.30   $76.30  
  Purchase #2 $149.50   6.385%   $159.0456   $159.05   $159.05   $159.00  
  Purchase #3 $123.67   10.209%   $136.2955   $136.30   $136.30   $136.30  
  Purchase #4 $202.31   3.586%   $209.5648   $209.56   $209.55   $209.60  
  Purchase #5 $139.71   5.309%   $147.1272   $147.13   $147.15   $147.10  
  Purchase #6 $40.94   3.488%   $42.368   $42.37   $42.35   $42.40  
  Purchase #7 $232.77   10.414%   $257.0107   $257.01   $257.00   $257.00  
  7 purchase totals = $956.18       $1,027.6945   $1,027.70   $1,027.70   $1,027.70