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 $44.93   5.199%   $47.2659   $47.27   $47.25   $47.30  
  Purchase #2 $48.58   12.756%   $54.7769   $54.78   $54.80   $54.80  
  Purchase #3 $91.36   6.703%   $97.4839   $97.48   $97.50   $97.50  
  Purchase #4 $118.87   11.710%   $132.7897   $132.79   $132.80   $132.80  
  Purchase #5 $195.29   6.495%   $207.9741   $207.97   $207.95   $208.00  
  Purchase #6 $135.72   5.672%   $143.418   $143.42   $143.40   $143.40  
  Purchase #7 $108.26   13.621%   $123.0061   $123.01   $123.00   $123.00  
  7 purchase totals = $743.01       $806.7146   $806.72   $806.70   $806.80