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 $161.93   4.400%   $169.0549   $169.05   $169.05   $169.10  
  Purchase #2 $131.42   8.531%   $142.6314   $142.63   $142.65   $142.60  
  Purchase #3 $156.48   12.805%   $176.5173   $176.52   $176.50   $176.50  
  Purchase #4 $244.87   6.661%   $261.1808   $261.18   $261.20   $261.20  
  Purchase #5 $171.66   7.762%   $184.9842   $184.98   $185.00   $185.00  
  Purchase #6 $247.60   11.817%   $276.8589   $276.86   $276.85   $276.90  
  Purchase #7 $16.83   9.580%   $18.4423   $18.44   $18.45   $18.40  
  7 purchase totals = $1,130.79       $1,229.6698   $1,229.66   $1,229.70   $1,229.70