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 $181.59   7.677%   $195.5307   $195.53   $195.55   $195.50  
  Purchase #2 $138.90   3.114%   $143.2253   $143.23   $143.25   $143.20  
  Purchase #3 $225.35   3.518%   $233.2778   $233.28   $233.30   $233.30  
  Purchase #4 $22.74   5.224%   $23.9279   $23.93   $23.95   $23.90  
  Purchase #5 $131.25   3.837%   $136.2861   $136.29   $136.30   $136.30  
  Purchase #6 $66.95   7.449%   $71.9371   $71.94   $71.95   $71.90  
  Purchase #7 $118.45   9.498%   $129.7004   $129.70   $129.70   $129.70  
  7 purchase totals = $885.23       $933.8853   $933.90   $934.00   $933.80