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 $87.83   6.356%   $93.4125   $93.41   $93.40   $93.40  
  Purchase #2 $168.32   10.327%   $185.7024   $185.70   $185.70   $185.70  
  Purchase #3 $160.53   11.426%   $178.8722   $178.87   $178.85   $178.90  
  Purchase #4 $110.82   8.484%   $120.222   $120.22   $120.20   $120.20  
  Purchase #5 $67.49   3.782%   $70.0425   $70.04   $70.05   $70.00  
  Purchase #6 $159.30   11.798%   $178.0942   $178.09   $178.10   $178.10  
  Purchase #7 $211.85   3.712%   $219.7139   $219.71   $219.70   $219.70  
  7 purchase totals = $966.14       $1,046.0597   $1,046.04   $1,046.00   $1,046.00