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 $246.89   6.602%   $263.1897   $263.19   $263.20   $263.20  
  Purchase #2 $98.89   4.456%   $103.2965   $103.30   $103.30   $103.30  
  Purchase #3 $231.55   10.535%   $255.9438   $255.94   $255.95   $255.90  
  Purchase #4 $78.79   11.698%   $88.0069   $88.01   $88.00   $88.00  
  Purchase #5 $219.97   6.211%   $233.6323   $233.63   $233.65   $233.60  
  Purchase #6 $137.36   6.205%   $145.8832   $145.88   $145.90   $145.90  
  Purchase #7 $75.97   10.852%   $84.2143   $84.21   $84.20   $84.20  
  7 purchase totals = $1,089.42       $1,174.1667   $1,174.16   $1,174.20   $1,174.10