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 $33.83   3.465%   $35.0022   $35.00   $35.00   $35.00  
  Purchase #2 $202.92   6.669%   $216.4527   $216.45   $216.45   $216.50  
  Purchase #3 $187.42   7.625%   $201.7108   $201.71   $201.70   $201.70  
  Purchase #4 $212.86   6.818%   $227.3728   $227.37   $227.35   $227.40  
  Purchase #5 $49.70   10.550%   $54.9434   $54.94   $54.95   $54.90  
  Purchase #6 $57.74   10.486%   $63.7946   $63.79   $63.80   $63.80  
  Purchase #7 $167.68   7.552%   $180.3432   $180.34   $180.35   $180.30  
  7 purchase totals = $912.15       $979.6197   $979.60   $979.60   $979.60