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 $155.38   13.817%   $176.8489   $176.85   $176.85   $176.80  
  Purchase #2 $72.48   3.494%   $75.0125   $75.01   $75.00   $75.00  
  Purchase #3 $91.86   6.647%   $97.9659   $97.97   $97.95   $98.00  
  Purchase #4 $57.35   7.659%   $61.7424   $61.74   $61.75   $61.70  
  Purchase #5 $17.68   4.840%   $18.5357   $18.54   $18.55   $18.50  
  Purchase #6 $89.29   5.514%   $94.2135   $94.21   $94.20   $94.20  
  Purchase #7 $90.53   12.194%   $101.5692   $101.57   $101.55   $101.60  
  7 purchase totals = $574.57       $625.8881   $625.89   $625.85   $625.80