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 $126.47   12.807%   $142.667   $142.67   $142.65   $142.70  
  Purchase #2 $246.82   13.258%   $279.5434   $279.54   $279.55   $279.50  
  Purchase #3 $23.31   6.207%   $24.7569   $24.76   $24.75   $24.80  
  Purchase #4 $171.95   13.667%   $195.4504   $195.45   $195.45   $195.50  
  Purchase #5 $36.80   3.420%   $38.0586   $38.06   $38.05   $38.10  
  Purchase #6 $44.86   9.394%   $49.0741   $49.07   $49.05   $49.10  
  Purchase #7 $216.91   7.453%   $233.0763   $233.08   $233.10   $233.10  
  7 purchase totals = $867.12       $962.6267   $962.63   $962.60   $962.80