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 $62.25   5.627%   $65.7528   $65.75   $65.75   $65.80  
  Purchase #2 $97.61   4.826%   $102.3207   $102.32   $102.30   $102.30  
  Purchase #3 $70.61   12.678%   $79.5619   $79.56   $79.55   $79.60  
  Purchase #4 $223.65   4.599%   $233.9357   $233.94   $233.95   $233.90  
  Purchase #5 $194.47   3.597%   $201.4651   $201.47   $201.45   $201.50  
  Purchase #6 $74.42   11.184%   $82.7431   $82.74   $82.75   $82.70  
  Purchase #7 $158.58   12.409%   $178.2582   $178.26   $178.25   $178.30  
  7 purchase totals = $881.59       $944.0375   $944.04   $944.00   $944.10