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 $180.97   7.730%   $194.959   $194.96   $194.95   $195.00  
  Purchase #2 $127.32   6.371%   $135.4316   $135.43   $135.45   $135.40  
  Purchase #3 $108.94   13.542%   $123.6927   $123.69   $123.70   $123.70  
  Purchase #4 $162.88   7.248%   $174.6855   $174.69   $174.70   $174.70  
  Purchase #5 $246.74   5.525%   $260.3724   $260.37   $260.35   $260.40  
  Purchase #6 $99.27   10.810%   $110.0011   $110.00   $110.00   $110.00  
  Purchase #7 $234.90   4.218%   $244.8081   $244.81   $244.80   $244.80  
  7 purchase totals = $1,161.02       $1,243.9504   $1,243.95   $1,243.95   $1,244.00