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 $82.96   7.504%   $89.1853   $89.19   $89.20   $89.20  
  Purchase #2 $235.91   6.153%   $250.4255   $250.43   $250.45   $250.40  
  Purchase #3 $214.62   3.638%   $222.4279   $222.43   $222.45   $222.40  
  Purchase #4 $209.63   6.666%   $223.6039   $223.60   $223.60   $223.60  
  Purchase #5 $171.61   9.343%   $187.6435   $187.64   $187.65   $187.60  
  Purchase #6 $193.47   11.548%   $215.8119   $215.81   $215.80   $215.80  
  Purchase #7 $13.65   3.157%   $14.0809   $14.08   $14.10   $14.10  
  7 purchase totals = $1,121.85       $1,203.1789   $1,203.18   $1,203.25   $1,203.10