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 $214.85   5.672%   $227.0363   $227.04   $227.05   $227.00  
  Purchase #2 $172.46   9.625%   $189.0593   $189.06   $189.05   $189.10  
  Purchase #3 $230.78   7.806%   $248.7947   $248.79   $248.80   $248.80  
  Purchase #4 $135.53   9.697%   $148.6723   $148.67   $148.65   $148.70  
  Purchase #5 $57.32   13.723%   $65.186   $65.19   $65.20   $65.20  
  Purchase #6 $146.35   12.315%   $164.373   $164.37   $164.35   $164.40  
  Purchase #7 $249.41   12.501%   $280.5887   $280.59   $280.60   $280.60  
  7 purchase totals = $1,206.70       $1,323.7103   $1,323.71   $1,323.70   $1,323.80