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 $59.53   6.361%   $63.3167   $63.32   $63.30   $63.30  
  Purchase #2 $189.32   8.722%   $205.8325   $205.83   $205.85   $205.80  
  Purchase #3 $136.92   13.701%   $155.6794   $155.68   $155.70   $155.70  
  Purchase #4 $127.68   13.682%   $145.1492   $145.15   $145.15   $145.10  
  Purchase #5 $137.79   5.385%   $145.21   $145.21   $145.20   $145.20  
  Purchase #6 $213.27   5.130%   $224.2108   $224.21   $224.20   $224.20  
  Purchase #7 $17.36   8.833%   $18.8934   $18.89   $18.90   $18.90  
  7 purchase totals = $881.87       $958.2920   $958.29   $958.30   $958.20