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 $93.93   8.141%   $101.5768   $101.58   $101.60   $101.60  
  Purchase #2 $145.51   7.709%   $156.7274   $156.73   $156.75   $156.70  
  Purchase #3 $243.94   12.297%   $273.9373   $273.94   $273.95   $273.90  
  Purchase #4 $231.78   4.421%   $242.027   $242.03   $242.05   $242.00  
  Purchase #5 $242.60   5.824%   $256.729   $256.73   $256.75   $256.70  
  Purchase #6 $10.68   6.315%   $11.3544   $11.35   $11.35   $11.40  
  Purchase #7 $141.87   9.210%   $154.9362   $154.94   $154.95   $154.90  
  7 purchase totals = $1,110.31       $1,197.2881   $1,197.30   $1,197.40   $1,197.20