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 $185.77   10.178%   $204.6777   $204.68   $204.70   $204.70  
  Purchase #2 $58.35   7.122%   $62.5057   $62.51   $62.50   $62.50  
  Purchase #3 $65.85   5.353%   $69.375   $69.38   $69.40   $69.40  
  Purchase #4 $139.31   9.135%   $152.036   $152.04   $152.05   $152.00  
  Purchase #5 $96.38   10.546%   $106.5442   $106.54   $106.55   $106.50  
  Purchase #6 $182.93   11.577%   $204.1078   $204.11   $204.10   $204.10  
  Purchase #7 $125.52   7.178%   $134.5298   $134.53   $134.55   $134.50  
  7 purchase totals = $854.11       $933.7762   $933.79   $933.85   $933.70