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 $190.50   10.857%   $211.1826   $211.18   $211.20   $211.20  
  Purchase #2 $5.36   8.530%   $5.8172   $5.82   $5.80   $5.80  
  Purchase #3 $6.67   10.262%   $7.3545   $7.35   $7.35   $7.40  
  Purchase #4 $12.29   3.216%   $12.6852   $12.69   $12.70   $12.70  
  Purchase #5 $180.72   8.294%   $195.7089   $195.71   $195.70   $195.70  
  Purchase #6 $21.25   9.378%   $23.2428   $23.24   $23.25   $23.20  
  Purchase #7 $203.44   12.120%   $228.0969   $228.10   $228.10   $228.10  
  7 purchase totals = $620.23       $684.0881   $684.09   $684.10   $684.10