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 $115.42   9.461%   $126.3399   $126.34   $126.35   $126.30  
  Purchase #2 $172.79   13.635%   $196.3499   $196.35   $196.35   $196.30  
  Purchase #3 $53.95   5.352%   $56.8374   $56.84   $56.85   $56.80  
  Purchase #4 $222.67   12.401%   $250.2833   $250.28   $250.30   $250.30  
  Purchase #5 $62.99   9.115%   $68.7315   $68.73   $68.75   $68.70  
  Purchase #6 $198.40   5.456%   $209.2247   $209.22   $209.20   $209.20  
  Purchase #7 $19.30   4.330%   $20.1357   $20.14   $20.15   $20.10  
  7 purchase totals = $845.52       $927.9024   $927.90   $927.95   $927.70