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 $211.82   3.699%   $219.6552   $219.66   $219.65   $219.70  
  Purchase #2 $111.55   5.648%   $117.8503   $117.85   $117.85   $117.90  
  Purchase #3 $22.64   11.530%   $25.2504   $25.25   $25.25   $25.30  
  Purchase #4 $235.63   11.414%   $262.5248   $262.52   $262.50   $262.50  
  Purchase #5 $175.30   10.663%   $193.9922   $193.99   $194.00   $194.00  
  Purchase #6 $102.31   12.602%   $115.2031   $115.20   $115.20   $115.20  
  Purchase #7 $241.29   10.776%   $267.2914   $267.29   $267.30   $267.30  
  7 purchase totals = $1,100.54       $1,201.7674   $1,201.76   $1,201.75   $1,201.90