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 $91.44   3.620%   $94.7501   $94.75   $94.75   $94.80  
  Purchase #2 $85.50   7.192%   $91.6492   $91.65   $91.65   $91.60  
  Purchase #3 $119.80   3.110%   $123.5258   $123.53   $123.55   $123.50  
  Purchase #4 $195.56   3.403%   $202.2149   $202.21   $202.20   $202.20  
  Purchase #5 $218.68   10.237%   $241.0663   $241.07   $241.05   $241.10  
  Purchase #6 $94.30   4.212%   $98.2719   $98.27   $98.25   $98.30  
  Purchase #7 $63.26   12.764%   $71.3345   $71.33   $71.35   $71.30  
  7 purchase totals = $868.54       $922.8127   $922.81   $922.80   $922.80