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 $182.90   12.374%   $205.532   $205.53   $205.55   $205.50  
  Purchase #2 $98.29   7.699%   $105.8573   $105.86   $105.85   $105.90  
  Purchase #3 $123.30   9.430%   $134.9272   $134.93   $134.95   $134.90  
  Purchase #4 $23.38   5.244%   $24.606   $24.61   $24.60   $24.60  
  Purchase #5 $143.79   11.278%   $160.0066   $160.01   $160.00   $160.00  
  Purchase #6 $87.77   4.121%   $91.387   $91.39   $91.40   $91.40  
  Purchase #7 $222.87   3.290%   $230.2024   $230.20   $230.20   $230.20  
  7 purchase totals = $882.30       $952.5185   $952.53   $952.55   $952.50