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   9.666%   $262.014   $262.01   $262.00   $262.00  
  Purchase #2 $157.43   8.567%   $170.917   $170.92   $170.90   $170.90  
  Purchase #3 $221.58   11.790%   $247.7043   $247.70   $247.70   $247.70  
  Purchase #4 $127.35   11.365%   $141.8233   $141.82   $141.80   $141.80  
  Purchase #5 $125.82   13.780%   $143.158   $143.16   $143.15   $143.20  
  Purchase #6 $141.98   9.117%   $154.9243   $154.92   $154.90   $154.90  
  Purchase #7 $8.37   11.689%   $9.3484   $9.35   $9.35   $9.30  
  7 purchase totals = $1,021.45       $1,129.8893   $1,129.88   $1,129.80   $1,129.80