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 $85.85   11.553%   $95.7683   $95.77   $95.75   $95.80  
  Purchase #2 $47.47   11.641%   $52.996   $53.00   $53.00   $53.00  
  Purchase #3 $220.77   11.364%   $245.8583   $245.86   $245.85   $245.90  
  Purchase #4 $105.41   4.503%   $110.1566   $110.16   $110.15   $110.20  
  Purchase #5 $244.35   4.373%   $255.0354   $255.04   $255.05   $255.00  
  Purchase #6 $81.50   3.746%   $84.553   $84.55   $84.55   $84.60  
  Purchase #7 $109.92   4.487%   $114.8521   $114.85   $114.85   $114.90  
  7 purchase totals = $895.27       $959.2197   $959.23   $959.20   $959.40