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 $208.99   11.293%   $232.5912   $232.59   $232.60   $232.60  
  Purchase #2 $164.39   10.371%   $181.4389   $181.44   $181.45   $181.40  
  Purchase #3 $204.29   7.512%   $219.6363   $219.64   $219.65   $219.60  
  Purchase #4 $160.97   7.484%   $173.017   $173.02   $173.00   $173.00  
  Purchase #5 $64.83   6.354%   $68.9493   $68.95   $68.95   $68.90  
  Purchase #6 $9.36   4.662%   $9.7964   $9.80   $9.80   $9.80  
  Purchase #7 $119.87   8.441%   $129.9882   $129.99   $130.00   $130.00  
  7 purchase totals = $932.70       $1,015.4173   $1,015.43   $1,015.45   $1,015.30