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 $71.64   7.117%   $76.7386   $76.74   $76.75   $76.70  
  Purchase #2 $191.59   5.859%   $202.8153   $202.82   $202.80   $202.80  
  Purchase #3 $164.61   11.217%   $183.0743   $183.07   $183.05   $183.10  
  Purchase #4 $44.35   12.740%   $50.0002   $50.00   $50.00   $50.00  
  Purchase #5 $219.67   4.551%   $229.6672   $229.67   $229.65   $229.70  
  Purchase #6 $91.43   4.695%   $95.7226   $95.72   $95.70   $95.70  
  Purchase #7 $154.77   4.513%   $161.7548   $161.75   $161.75   $161.80  
  7 purchase totals = $938.06       $999.7730   $999.77   $999.70   $999.80