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 $49.68   9.394%   $54.3469   $54.35   $54.35   $54.30  
  Purchase #2 $149.25   3.404%   $154.3305   $154.33   $154.35   $154.30  
  Purchase #3 $244.44   9.794%   $268.3805   $268.38   $268.40   $268.40  
  Purchase #4 $57.32   12.157%   $64.2884   $64.29   $64.30   $64.30  
  Purchase #5 $101.74   4.124%   $105.9358   $105.94   $105.95   $105.90  
  Purchase #6 $9.54   13.404%   $10.8187   $10.82   $10.80   $10.80  
  Purchase #7 $65.32   13.586%   $74.1944   $74.19   $74.20   $74.20  
  7 purchase totals = $677.29       $732.2952   $732.30   $732.35   $732.20