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 $111.53   12.288%   $125.2348   $125.23   $125.25   $125.20  
  Purchase #2 $102.45   6.398%   $109.0048   $109.00   $109.00   $109.00  
  Purchase #3 $73.83   7.766%   $79.5636   $79.56   $79.55   $79.60  
  Purchase #4 $88.98   12.204%   $99.8391   $99.84   $99.85   $99.80  
  Purchase #5 $216.70   12.726%   $244.2772   $244.28   $244.30   $244.30  
  Purchase #6 $194.61   8.454%   $211.0623   $211.06   $211.05   $211.10  
  Purchase #7 $118.66   12.164%   $133.0938   $133.09   $133.10   $133.10  
  7 purchase totals = $906.76       $1,002.0756   $1,002.06   $1,002.10   $1,002.10