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 $217.42   13.721%   $247.2522   $247.25   $247.25   $247.30  
  Purchase #2 $53.71   5.143%   $56.4723   $56.47   $56.45   $56.50  
  Purchase #3 $193.58   9.515%   $211.9991   $212.00   $212.00   $212.00  
  Purchase #4 $193.77   6.285%   $205.9484   $205.95   $205.95   $205.90  
  Purchase #5 $15.91   4.696%   $16.6571   $16.66   $16.65   $16.70  
  Purchase #6 $106.63   7.656%   $114.7936   $114.79   $114.80   $114.80  
  Purchase #7 $157.94   7.119%   $169.1837   $169.18   $169.20   $169.20  
  7 purchase totals = $938.96       $1,022.3064   $1,022.30   $1,022.30   $1,022.40