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 $55.42   11.701%   $61.9047   $61.90   $61.90   $61.90  
  Purchase #2 $170.62   13.853%   $194.256   $194.26   $194.25   $194.30  
  Purchase #3 $57.51   13.364%   $65.1956   $65.20   $65.20   $65.20  
  Purchase #4 $84.98   4.775%   $89.0378   $89.04   $89.05   $89.00  
  Purchase #5 $58.37   10.211%   $64.3302   $64.33   $64.35   $64.30  
  Purchase #6 $160.72   8.811%   $174.881   $174.88   $174.90   $174.90  
  Purchase #7 $44.64   6.786%   $47.6693   $47.67   $47.65   $47.70  
  7 purchase totals = $632.26       $697.2746   $697.28   $697.30   $697.30