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 $82.27   13.745%   $93.578   $93.58   $93.60   $93.60  
  Purchase #2 $193.65   4.387%   $202.1454   $202.15   $202.15   $202.10  
  Purchase #3 $80.59   5.629%   $85.1264   $85.13   $85.15   $85.10  
  Purchase #4 $147.63   6.790%   $157.6541   $157.65   $157.65   $157.70  
  Purchase #5 $22.74   11.485%   $25.3517   $25.35   $25.35   $25.40  
  Purchase #6 $250.86   12.661%   $282.6214   $282.62   $282.60   $282.60  
  Purchase #7 $59.26   13.566%   $67.2992   $67.30   $67.30   $67.30  
  7 purchase totals = $837.00       $913.7762   $913.78   $913.80   $913.80