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 $162.67   8.684%   $176.7963   $176.80   $176.80   $176.80  
  Purchase #2 $77.37   9.437%   $84.6714   $84.67   $84.65   $84.70  
  Purchase #3 $9.90   11.135%   $11.0024   $11.00   $11.00   $11.00  
  Purchase #4 $215.63   12.462%   $242.5018   $242.50   $242.50   $242.50  
  Purchase #5 $105.33   11.510%   $117.4535   $117.45   $117.45   $117.50  
  Purchase #6 $184.61   10.713%   $204.3873   $204.39   $204.40   $204.40  
  Purchase #7 $216.25   3.763%   $224.3875   $224.39   $224.40   $224.40  
  7 purchase totals = $971.76       $1,061.2002   $1,061.20   $1,061.20   $1,061.30