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 $223.66   5.655%   $236.308   $236.31   $236.30   $236.30  
  Purchase #2 $23.85   12.715%   $26.8825   $26.88   $26.90   $26.90  
  Purchase #3 $34.84   8.468%   $37.7903   $37.79   $37.80   $37.80  
  Purchase #4 $184.54   8.737%   $200.6633   $200.66   $200.65   $200.70  
  Purchase #5 $164.85   5.491%   $173.9019   $173.90   $173.90   $173.90  
  Purchase #6 $78.26   9.658%   $85.8184   $85.82   $85.80   $85.80  
  Purchase #7 $203.64   3.596%   $210.9629   $210.96   $210.95   $211.00  
  7 purchase totals = $913.64       $972.3273   $972.32   $972.30   $972.40