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 $136.75   8.384%   $148.2151   $148.22   $148.20   $148.20  
  Purchase #2 $172.29   7.493%   $185.1997   $185.20   $185.20   $185.20  
  Purchase #3 $204.83   8.714%   $222.6789   $222.68   $222.70   $222.70  
  Purchase #4 $240.30   8.830%   $261.5185   $261.52   $261.50   $261.50  
  Purchase #5 $208.90   7.198%   $223.9366   $223.94   $223.95   $223.90  
  Purchase #6 $144.81   7.811%   $156.1211   $156.12   $156.10   $156.10  
  Purchase #7 $209.41   11.302%   $233.0775   $233.08   $233.10   $233.10  
  7 purchase totals = $1,317.29       $1,430.7474   $1,430.76   $1,430.75   $1,430.70