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 $114.85   9.714%   $126.0065   $126.01   $126.00   $126.00  
  Purchase #2 $35.39   10.667%   $39.1651   $39.17   $39.15   $39.20  
  Purchase #3 $128.85   6.591%   $137.3425   $137.34   $137.35   $137.30  
  Purchase #4 $232.94   5.461%   $245.6609   $245.66   $245.65   $245.70  
  Purchase #5 $181.46   6.685%   $193.5906   $193.59   $193.60   $193.60  
  Purchase #6 $19.43   3.165%   $20.045   $20.05   $20.05   $20.00  
  Purchase #7 $42.40   3.186%   $43.7509   $43.75   $43.75   $43.80  
  7 purchase totals = $755.32       $805.5615   $805.57   $805.55   $805.60