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 $48.59   9.452%   $53.1827   $53.18   $53.20   $53.20  
  Purchase #2 $22.66   5.786%   $23.9711   $23.97   $23.95   $24.00  
  Purchase #3 $153.67   8.793%   $167.1822   $167.18   $167.20   $167.20  
  Purchase #4 $89.34   12.342%   $100.3663   $100.37   $100.35   $100.40  
  Purchase #5 $74.65   10.499%   $82.4875   $82.49   $82.50   $82.50  
  Purchase #6 $224.33   11.283%   $249.6412   $249.64   $249.65   $249.60  
  Purchase #7 $248.25   11.238%   $276.1483   $276.15   $276.15   $276.10  
  7 purchase totals = $861.49       $952.9793   $952.98   $953.00   $953.00