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 $62.45   4.802%   $65.4488   $65.45   $65.45   $65.40  
  Purchase #2 $247.64   4.224%   $258.1003   $258.10   $258.10   $258.10  
  Purchase #3 $97.52   11.734%   $108.963   $108.96   $108.95   $109.00  
  Purchase #4 $14.75   4.448%   $15.4061   $15.41   $15.40   $15.40  
  Purchase #5 $103.75   9.496%   $113.6021   $113.60   $113.60   $113.60  
  Purchase #6 $170.76   12.410%   $191.9513   $191.95   $191.95   $192.00  
  Purchase #7 $26.87   7.702%   $28.9395   $28.94   $28.95   $28.90  
  7 purchase totals = $723.74       $782.4111   $782.41   $782.40   $782.40