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 $56.28   9.333%   $61.5326   $61.53   $61.55   $61.50  
  Purchase #2 $186.76   9.406%   $204.3266   $204.33   $204.35   $204.30  
  Purchase #3 $120.91   4.652%   $126.5347   $126.53   $126.55   $126.50  
  Purchase #4 $66.47   5.139%   $69.8859   $69.89   $69.90   $69.90  
  Purchase #5 $205.75   7.288%   $220.7451   $220.75   $220.75   $220.70  
  Purchase #6 $195.48   9.362%   $213.7808   $213.78   $213.80   $213.80  
  Purchase #7 $131.28   9.675%   $143.9813   $143.98   $144.00   $144.00  
  7 purchase totals = $962.93       $1,040.7870   $1,040.79   $1,040.90   $1,040.70