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 $238.92   6.568%   $254.6123   $254.61   $254.60   $254.60  
  Purchase #2 $108.77   8.709%   $118.2428   $118.24   $118.25   $118.20  
  Purchase #3 $48.82   4.459%   $50.9969   $51.00   $51.00   $51.00  
  Purchase #4 $106.56   7.520%   $114.5733   $114.57   $114.55   $114.60  
  Purchase #5 $231.62   5.616%   $244.6278   $244.63   $244.65   $244.60  
  Purchase #6 $188.81   12.285%   $212.0053   $212.01   $212.00   $212.00  
  Purchase #7 $245.49   9.624%   $269.116   $269.12   $269.10   $269.10  
  7 purchase totals = $1,168.99       $1,264.1744   $1,264.18   $1,264.15   $1,264.10