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 $202.66   13.633%   $230.2886   $230.29   $230.30   $230.30  
  Purchase #2 $58.92   10.402%   $65.0489   $65.05   $65.05   $65.00  
  Purchase #3 $222.58   11.463%   $248.0943   $248.09   $248.10   $248.10  
  Purchase #4 $121.71   3.736%   $126.2571   $126.26   $126.25   $126.30  
  Purchase #5 $164.63   5.391%   $173.5052   $173.51   $173.50   $173.50  
  Purchase #6 $117.81   12.561%   $132.6081   $132.61   $132.60   $132.60  
  Purchase #7 $23.78   5.686%   $25.1321   $25.13   $25.15   $25.10  
  7 purchase totals = $912.09       $1,000.9343   $1,000.94   $1,000.95   $1,000.90