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 $56.94   8.838%   $61.9724   $61.97   $61.95   $62.00  
  Purchase #2 $205.36   3.554%   $212.6585   $212.66   $212.65   $212.70  
  Purchase #3 $79.65   10.238%   $87.8046   $87.80   $87.80   $87.80  
  Purchase #4 $215.43   13.833%   $245.2304   $245.23   $245.25   $245.20  
  Purchase #5 $115.27   8.701%   $125.2996   $125.30   $125.30   $125.30  
  Purchase #6 $39.35   6.798%   $42.025   $42.03   $42.05   $42.00  
  Purchase #7 $27.39   9.793%   $30.0723   $30.07   $30.05   $30.10  
  7 purchase totals = $739.39       $805.0628   $805.06   $805.05   $805.10