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 $114.42   5.469%   $120.6776   $120.68   $120.70   $120.70  
  Purchase #2 $98.75   11.715%   $110.3186   $110.32   $110.30   $110.30  
  Purchase #3 $126.66   7.538%   $136.2076   $136.21   $136.20   $136.20  
  Purchase #4 $141.49   10.839%   $156.8261   $156.83   $156.85   $156.80  
  Purchase #5 $153.33   12.275%   $172.1513   $172.15   $172.15   $172.20  
  Purchase #6 $217.32   11.316%   $241.9119   $241.91   $241.90   $241.90  
  Purchase #7 $112.65   8.494%   $122.2185   $122.22   $122.20   $122.20  
  7 purchase totals = $964.62       $1,060.3116   $1,060.32   $1,060.30   $1,060.30