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 $54.31   8.506%   $58.9296   $58.93   $58.95   $58.90  
  Purchase #2 $145.87   11.678%   $162.9047   $162.90   $162.90   $162.90  
  Purchase #3 $138.46   4.571%   $144.789   $144.79   $144.80   $144.80  
  Purchase #4 $198.41   9.471%   $217.2014   $217.20   $217.20   $217.20  
  Purchase #5 $162.88   13.810%   $185.3737   $185.37   $185.35   $185.40  
  Purchase #6 $126.42   5.348%   $133.1809   $133.18   $133.20   $133.20  
  Purchase #7 $158.50   3.346%   $163.8034   $163.80   $163.80   $163.80  
  7 purchase totals = $984.85       $1,066.1827   $1,066.17   $1,066.20   $1,066.20