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 $249.25   10.154%   $274.5588   $274.56   $274.55   $274.60  
  Purchase #2 $124.58   7.236%   $133.5946   $133.59   $133.60   $133.60  
  Purchase #3 $156.49   6.739%   $167.0359   $167.04   $167.05   $167.00  
  Purchase #4 $96.82   7.488%   $104.0699   $104.07   $104.05   $104.10  
  Purchase #5 $143.74   5.290%   $151.3438   $151.34   $151.35   $151.30  
  Purchase #6 $49.77   5.162%   $52.3391   $52.34   $52.35   $52.30  
  Purchase #7 $142.28   13.751%   $161.8449   $161.84   $161.85   $161.80  
  7 purchase totals = $962.93       $1,044.7870   $1,044.78   $1,044.80   $1,044.70