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 $61.55   9.641%   $67.484   $67.48   $67.50   $67.50  
  Purchase #2 $14.35   11.722%   $16.0321   $16.03   $16.05   $16.00  
  Purchase #3 $120.98   10.669%   $133.8874   $133.89   $133.90   $133.90  
  Purchase #4 $149.35   8.467%   $161.9955   $162.00   $162.00   $162.00  
  Purchase #5 $38.95   8.210%   $42.1478   $42.15   $42.15   $42.10  
  Purchase #6 $131.25   13.798%   $149.3599   $149.36   $149.35   $149.40  
  Purchase #7 $170.70   8.186%   $184.6735   $184.67   $184.65   $184.70  
  7 purchase totals = $687.13       $755.5802   $755.58   $755.60   $755.60