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 $53.71   4.836%   $56.3074   $56.31   $56.30   $56.30  
  Purchase #2 $26.89   11.206%   $29.9033   $29.90   $29.90   $29.90  
  Purchase #3 $36.77   12.850%   $41.4949   $41.49   $41.50   $41.50  
  Purchase #4 $210.42   7.106%   $225.3724   $225.37   $225.35   $225.40  
  Purchase #5 $106.48   6.352%   $113.2436   $113.24   $113.25   $113.20  
  Purchase #6 $233.85   3.746%   $242.61   $242.61   $242.60   $242.60  
  Purchase #7 $45.89   6.203%   $48.7366   $48.74   $48.75   $48.70  
  7 purchase totals = $714.01       $757.6682   $757.66   $757.65   $757.60