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 $236.92   8.782%   $257.7263   $257.73   $257.75   $257.70  
  Purchase #2 $223.35   4.527%   $233.4611   $233.46   $233.45   $233.50  
  Purchase #3 $117.58   6.224%   $124.8982   $124.90   $124.90   $124.90  
  Purchase #4 $239.60   6.809%   $255.9144   $255.91   $255.90   $255.90  
  Purchase #5 $159.67   3.574%   $165.3766   $165.38   $165.40   $165.40  
  Purchase #6 $207.51   11.203%   $230.7573   $230.76   $230.75   $230.80  
  Purchase #7 $156.74   12.263%   $175.961   $175.96   $175.95   $176.00  
  7 purchase totals = $1,341.37       $1,444.0949   $1,444.10   $1,444.10   $1,444.20