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 $204.73   10.497%   $226.2205   $226.22   $226.20   $226.20  
  Purchase #2 $57.84   3.358%   $59.7823   $59.78   $59.80   $59.80  
  Purchase #3 $119.47   13.439%   $135.5256   $135.53   $135.55   $135.50  
  Purchase #4 $36.95   5.232%   $38.8832   $38.88   $38.90   $38.90  
  Purchase #5 $185.28   3.215%   $191.2368   $191.24   $191.25   $191.20  
  Purchase #6 $96.50   8.823%   $105.0142   $105.01   $105.00   $105.00  
  Purchase #7 $247.36   11.326%   $275.376   $275.38   $275.40   $275.40  
  7 purchase totals = $948.13       $1,032.0386   $1,032.04   $1,032.10   $1,032.00