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 $89.98   5.805%   $95.2033   $95.20   $95.20   $95.20  
  Purchase #2 $198.81   12.128%   $222.9217   $222.92   $222.90   $222.90  
  Purchase #3 $212.28   7.475%   $228.1479   $228.15   $228.15   $228.10  
  Purchase #4 $85.97   11.562%   $95.9099   $95.91   $95.90   $95.90  
  Purchase #5 $183.80   12.731%   $207.1996   $207.20   $207.20   $207.20  
  Purchase #6 $209.76   10.472%   $231.7261   $231.73   $231.75   $231.70  
  Purchase #7 $179.46   7.707%   $193.291   $193.29   $193.30   $193.30  
  7 purchase totals = $1,160.06       $1,274.3995   $1,274.40   $1,274.40   $1,274.30