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 $83.35   11.492%   $92.9286   $92.93   $92.95   $92.90  
  Purchase #2 $186.48   3.872%   $193.7005   $193.70   $193.70   $193.70  
  Purchase #3 $37.88   8.249%   $41.0047   $41.00   $41.00   $41.00  
  Purchase #4 $75.49   9.414%   $82.5966   $82.60   $82.60   $82.60  
  Purchase #5 $200.75   9.487%   $219.7952   $219.80   $219.80   $219.80  
  Purchase #6 $75.56   12.724%   $85.1743   $85.17   $85.15   $85.20  
  Purchase #7 $28.31   11.720%   $31.6279   $31.63   $31.65   $31.60  
  7 purchase totals = $687.82       $746.8278   $746.83   $746.85   $746.80