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 $103.79   10.773%   $114.9713   $114.97   $114.95   $115.00  
  Purchase #2 $153.28   4.165%   $159.6641   $159.66   $159.65   $159.70  
  Purchase #3 $102.35   3.172%   $105.5965   $105.60   $105.60   $105.60  
  Purchase #4 $245.31   9.258%   $268.0208   $268.02   $268.00   $268.00  
  Purchase #5 $211.41   12.329%   $237.4747   $237.47   $237.45   $237.50  
  Purchase #6 $48.65   5.829%   $51.4858   $51.49   $51.50   $51.50  
  Purchase #7 $11.88   6.486%   $12.6505   $12.65   $12.65   $12.70  
  7 purchase totals = $876.67       $949.8637   $949.86   $949.80   $950.00