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 $64.40   13.163%   $72.877   $72.88   $72.90   $72.90  
  Purchase #2 $111.26   12.171%   $124.8015   $124.80   $124.80   $124.80  
  Purchase #3 $94.60   3.161%   $97.5903   $97.59   $97.60   $97.60  
  Purchase #4 $65.99   12.535%   $74.2618   $74.26   $74.25   $74.30  
  Purchase #5 $192.40   6.494%   $204.8945   $204.89   $204.90   $204.90  
  Purchase #6 $5.62   5.554%   $5.9321   $5.93   $5.95   $5.90  
  Purchase #7 $189.58   6.300%   $201.5235   $201.52   $201.50   $201.50  
  7 purchase totals = $723.85       $781.8807   $781.87   $781.90   $781.90