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 $54.66   3.517%   $56.5824   $56.58   $56.60   $56.60  
  Purchase #2 $136.34   9.188%   $148.8669   $148.87   $148.85   $148.90  
  Purchase #3 $147.68   5.222%   $155.3918   $155.39   $155.40   $155.40  
  Purchase #4 $92.85   5.173%   $97.6531   $97.65   $97.65   $97.70  
  Purchase #5 $69.77   8.108%   $75.427   $75.43   $75.45   $75.40  
  Purchase #6 $89.94   4.610%   $94.0862   $94.09   $94.10   $94.10  
  Purchase #7 $115.67   8.800%   $125.849   $125.85   $125.85   $125.80  
  7 purchase totals = $706.91       $753.8564   $753.86   $753.90   $753.90