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 $156.85   12.691%   $176.7558   $176.76   $176.75   $176.80  
  Purchase #2 $59.33   9.319%   $64.859   $64.86   $64.85   $64.90  
  Purchase #3 $224.41   8.366%   $243.1841   $243.18   $243.20   $243.20  
  Purchase #4 $205.46   13.843%   $233.9018   $233.90   $233.90   $233.90  
  Purchase #5 $238.87   6.520%   $254.4443   $254.44   $254.45   $254.40  
  Purchase #6 $218.65   13.814%   $248.8543   $248.85   $248.85   $248.90  
  Purchase #7 $231.70   7.662%   $249.4529   $249.45   $249.45   $249.50  
  7 purchase totals = $1,335.27       $1,471.4522   $1,471.44   $1,471.45   $1,471.60