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 $213.67   13.581%   $242.6885   $242.69   $242.70   $242.70  
  Purchase #2 $131.98   11.278%   $146.8647   $146.86   $146.85   $146.90  
  Purchase #3 $118.96   4.586%   $124.4155   $124.42   $124.40   $124.40  
  Purchase #4 $183.54   4.581%   $191.948   $191.95   $191.95   $191.90  
  Purchase #5 $104.58   12.613%   $117.7707   $117.77   $117.75   $117.80  
  Purchase #6 $231.80   3.426%   $239.7415   $239.74   $239.75   $239.70  
  Purchase #7 $131.66   5.512%   $138.9171   $138.92   $138.90   $138.90  
  7 purchase totals = $1,116.19       $1,202.3460   $1,202.35   $1,202.30   $1,202.30