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 $233.33   10.556%   $257.9603   $257.96   $257.95   $258.00  
  Purchase #2 $221.78   5.219%   $233.3547   $233.35   $233.35   $233.40  
  Purchase #3 $241.29   3.551%   $249.8582   $249.86   $249.85   $249.90  
  Purchase #4 $79.78   3.425%   $82.5125   $82.51   $82.50   $82.50  
  Purchase #5 $23.70   8.612%   $25.741   $25.74   $25.75   $25.70  
  Purchase #6 $158.58   10.225%   $174.7948   $174.79   $174.80   $174.80  
  Purchase #7 $82.74   13.169%   $93.636   $93.64   $93.65   $93.60  
  7 purchase totals = $1,041.20       $1,117.8575   $1,117.85   $1,117.85   $1,117.90