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 $241.53   11.707%   $269.8059   $269.81   $269.80   $269.80  
  Purchase #2 $183.64   6.347%   $195.2956   $195.30   $195.30   $195.30  
  Purchase #3 $242.87   10.288%   $267.8565   $267.86   $267.85   $267.90  
  Purchase #4 $100.31   6.472%   $106.8021   $106.80   $106.80   $106.80  
  Purchase #5 $213.43   6.270%   $226.8121   $226.81   $226.80   $226.80  
  Purchase #6 $145.71   13.122%   $164.8301   $164.83   $164.85   $164.80  
  Purchase #7 $157.47   5.366%   $165.9198   $165.92   $165.90   $165.90  
  7 purchase totals = $1,284.96       $1,397.3221   $1,397.33   $1,397.30   $1,397.30