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 $228.47   3.219%   $235.8244   $235.82   $235.80   $235.80  
  Purchase #2 $56.97   9.600%   $62.4391   $62.44   $62.45   $62.40  
  Purchase #3 $120.54   3.680%   $124.9759   $124.98   $125.00   $125.00  
  Purchase #4 $169.78   11.515%   $189.3302   $189.33   $189.35   $189.30  
  Purchase #5 $75.34   10.267%   $83.0752   $83.08   $83.10   $83.10  
  Purchase #6 $182.59   7.172%   $195.6854   $195.69   $195.70   $195.70  
  Purchase #7 $129.44   3.108%   $133.463   $133.46   $133.45   $133.50  
  7 purchase totals = $963.13       $1,024.7932   $1,024.80   $1,024.85   $1,024.80