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 $190.87   13.237%   $216.1355   $216.14   $216.15   $216.10  
  Purchase #2 $236.54   3.662%   $245.2021   $245.20   $245.20   $245.20  
  Purchase #3 $137.29   5.405%   $144.7105   $144.71   $144.70   $144.70  
  Purchase #4 $127.41   4.633%   $133.3129   $133.31   $133.30   $133.30  
  Purchase #5 $31.99   10.579%   $35.3742   $35.37   $35.35   $35.40  
  Purchase #6 $166.81   12.148%   $187.0741   $187.07   $187.05   $187.10  
  Purchase #7 $36.75   3.430%   $38.0105   $38.01   $38.00   $38.00  
  7 purchase totals = $927.66       $999.8198   $999.81   $999.75   $999.80