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 $202.76   8.135%   $219.2545   $219.25   $219.25   $219.30  
  Purchase #2 $149.46   4.593%   $156.3247   $156.32   $156.30   $156.30  
  Purchase #3 $224.34   3.394%   $231.9541   $231.95   $231.95   $232.00  
  Purchase #4 $61.27   13.648%   $69.6321   $69.63   $69.65   $69.60  
  Purchase #5 $126.56   4.220%   $131.9008   $131.90   $131.90   $131.90  
  Purchase #6 $194.87   7.447%   $209.382   $209.38   $209.40   $209.40  
  Purchase #7 $46.91   9.463%   $51.3491   $51.35   $51.35   $51.30  
  7 purchase totals = $1,006.17       $1,069.7973   $1,069.78   $1,069.80   $1,069.80