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 $100.34   13.425%   $113.8106   $113.81   $113.80   $113.80  
  Purchase #2 $100.71   4.271%   $105.0113   $105.01   $105.00   $105.00  
  Purchase #3 $95.66   12.230%   $107.3592   $107.36   $107.35   $107.40  
  Purchase #4 $145.48   3.390%   $150.4118   $150.41   $150.40   $150.40  
  Purchase #5 $128.26   8.145%   $138.7068   $138.71   $138.70   $138.70  
  Purchase #6 $41.75   7.440%   $44.8562   $44.86   $44.85   $44.90  
  Purchase #7 $16.89   5.499%   $17.8188   $17.82   $17.80   $17.80  
  7 purchase totals = $629.09       $677.9747   $677.98   $677.90   $678.00