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 $76.76   11.602%   $85.6657   $85.67   $85.65   $85.70  
  Purchase #2 $97.83   3.472%   $101.2267   $101.23   $101.25   $101.20  
  Purchase #3 $131.59   4.424%   $137.4115   $137.41   $137.40   $137.40  
  Purchase #4 $211.33   10.555%   $233.6359   $233.64   $233.65   $233.60  
  Purchase #5 $225.86   12.444%   $253.966   $253.97   $253.95   $254.00  
  Purchase #6 $152.46   5.725%   $161.1883   $161.19   $161.20   $161.20  
  Purchase #7 $235.66   4.677%   $246.6818   $246.68   $246.70   $246.70  
  7 purchase totals = $1,131.49       $1,219.7759   $1,219.79   $1,219.80   $1,219.80