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 $54.58   10.468%   $60.2934   $60.29   $60.30   $60.30  
  Purchase #2 $82.76   10.696%   $91.612   $91.61   $91.60   $91.60  
  Purchase #3 $95.66   9.153%   $104.4158   $104.42   $104.40   $104.40  
  Purchase #4 $29.42   8.557%   $31.9375   $31.94   $31.95   $31.90  
  Purchase #5 $215.48   12.170%   $241.7039   $241.70   $241.70   $241.70  
  Purchase #6 $50.35   12.358%   $56.5723   $56.57   $56.55   $56.60  
  Purchase #7 $103.43   5.238%   $108.8477   $108.85   $108.85   $108.80  
  7 purchase totals = $631.68       $695.3826   $695.38   $695.35   $695.30