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 $192.66   9.696%   $211.3403   $211.34   $211.35   $211.30  
  Purchase #2 $199.35   11.287%   $221.8506   $221.85   $221.85   $221.90  
  Purchase #3 $109.89   8.535%   $119.2691   $119.27   $119.25   $119.30  
  Purchase #4 $34.94   12.378%   $39.2649   $39.26   $39.25   $39.30  
  Purchase #5 $125.25   3.200%   $129.258   $129.26   $129.25   $129.30  
  Purchase #6 $46.84   6.332%   $49.8059   $49.81   $49.80   $49.80  
  Purchase #7 $162.98   9.534%   $178.5185   $178.52   $178.50   $178.50  
  7 purchase totals = $871.91       $949.3073   $949.31   $949.25   $949.40