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 $173.51   13.366%   $196.7013   $196.70   $196.70   $196.70  
  Purchase #2 $242.56   13.387%   $275.0315   $275.03   $275.05   $275.00  
  Purchase #3 $95.33   7.554%   $102.5312   $102.53   $102.55   $102.50  
  Purchase #4 $173.49   12.286%   $194.805   $194.81   $194.80   $194.80  
  Purchase #5 $68.61   11.695%   $76.6339   $76.63   $76.65   $76.60  
  Purchase #6 $181.59   9.198%   $198.2926   $198.29   $198.30   $198.30  
  Purchase #7 $235.58   5.277%   $248.0116   $248.01   $248.00   $248.00  
  7 purchase totals = $1,170.67       $1,292.0071   $1,292.00   $1,292.05   $1,291.90