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 $84.83   13.436%   $96.2278   $96.23   $96.25   $96.20  
  Purchase #2 $51.42   7.366%   $55.2076   $55.21   $55.20   $55.20  
  Purchase #3 $189.37   4.386%   $197.6758   $197.68   $197.70   $197.70  
  Purchase #4 $120.34   4.214%   $125.4111   $125.41   $125.40   $125.40  
  Purchase #5 $27.45   10.638%   $30.3701   $30.37   $30.35   $30.40  
  Purchase #6 $75.87   6.657%   $80.9207   $80.92   $80.90   $80.90  
  Purchase #7 $62.93   12.653%   $70.8925   $70.89   $70.90   $70.90  
  7 purchase totals = $612.21       $656.7056   $656.71   $656.70   $656.70