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 $31.45   4.702%   $32.9288   $32.93   $32.95   $32.90  
  Purchase #2 $57.41   13.564%   $65.1971   $65.20   $65.20   $65.20  
  Purchase #3 $30.29   13.831%   $34.4794   $34.48   $34.50   $34.50  
  Purchase #4 $206.80   8.645%   $224.6779   $224.68   $224.70   $224.70  
  Purchase #5 $41.90   5.356%   $44.1442   $44.14   $44.15   $44.10  
  Purchase #6 $189.76   13.128%   $214.6717   $214.67   $214.65   $214.70  
  Purchase #7 $58.35   11.153%   $64.8578   $64.86   $64.85   $64.90  
  7 purchase totals = $615.96       $680.9569   $680.96   $681.00   $681.00