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 $188.95   7.548%   $203.2119   $203.21   $203.20   $203.20  
  Purchase #2 $249.80   6.204%   $265.2976   $265.30   $265.30   $265.30  
  Purchase #3 $51.39   6.638%   $54.8013   $54.80   $54.80   $54.80  
  Purchase #4 $186.25   6.133%   $197.6727   $197.67   $197.65   $197.70  
  Purchase #5 $232.31   5.369%   $244.7827   $244.78   $244.80   $244.80  
  Purchase #6 $154.25   12.136%   $172.9698   $172.97   $172.95   $173.00  
  Purchase #7 $116.27   3.468%   $120.3022   $120.30   $120.30   $120.30  
  7 purchase totals = $1,179.22       $1,259.0382   $1,259.03   $1,259.00   $1,259.10