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 $214.38   13.822%   $244.0116   $244.01   $244.00   $244.00  
  Purchase #2 $209.80   11.205%   $233.3081   $233.31   $233.30   $233.30  
  Purchase #3 $99.32   13.209%   $112.4392   $112.44   $112.45   $112.40  
  Purchase #4 $181.55   12.796%   $204.7811   $204.78   $204.80   $204.80  
  Purchase #5 $113.37   6.227%   $120.4295   $120.43   $120.45   $120.40  
  Purchase #6 $143.59   11.455%   $160.0382   $160.04   $160.05   $160.00  
  Purchase #7 $44.66   11.236%   $49.678   $49.68   $49.70   $49.70  
  7 purchase totals = $1,006.67       $1,124.6857   $1,124.69   $1,124.75   $1,124.60