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 $205.46   11.689%   $229.4762   $229.48   $229.50   $229.50  
  Purchase #2 $229.96   6.247%   $244.3256   $244.33   $244.35   $244.30  
  Purchase #3 $224.97   3.480%   $232.799   $232.80   $232.80   $232.80  
  Purchase #4 $189.96   12.524%   $213.7506   $213.75   $213.75   $213.80  
  Purchase #5 $82.85   11.618%   $92.4755   $92.48   $92.50   $92.50  
  Purchase #6 $117.85   13.272%   $133.4911   $133.49   $133.50   $133.50  
  Purchase #7 $120.96   4.181%   $126.0173   $126.02   $126.00   $126.00  
  7 purchase totals = $1,172.01       $1,272.3353   $1,272.35   $1,272.40   $1,272.40