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 $68.31   10.791%   $75.6813   $75.68   $75.70   $75.70  
  Purchase #2 $171.94   10.476%   $189.9524   $189.95   $189.95   $190.00  
  Purchase #3 $143.48   9.636%   $157.3057   $157.31   $157.30   $157.30  
  Purchase #4 $230.85   9.479%   $252.7323   $252.73   $252.75   $252.70  
  Purchase #5 $24.30   13.186%   $27.5042   $27.50   $27.50   $27.50  
  Purchase #6 $160.37   11.271%   $178.4453   $178.45   $178.45   $178.40  
  Purchase #7 $49.64   5.446%   $52.3434   $52.34   $52.35   $52.30  
  7 purchase totals = $848.89       $933.9646   $933.96   $934.00   $933.90