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 $99.53   13.643%   $113.1089   $113.11   $113.10   $113.10  
  Purchase #2 $11.31   7.791%   $12.1912   $12.19   $12.20   $12.20  
  Purchase #3 $7.27   7.290%   $7.8   $7.80   $7.80   $7.80  
  Purchase #4 $85.52   11.787%   $95.6002   $95.60   $95.60   $95.60  
  Purchase #5 $174.66   13.116%   $197.5684   $197.57   $197.55   $197.60  
  Purchase #6 $144.42   5.188%   $151.9125   $151.91   $151.90   $151.90  
  Purchase #7 $227.37   7.652%   $244.7684   $244.77   $244.75   $244.80  
  7 purchase totals = $750.08       $822.9496   $822.95   $822.90   $823.00