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 $180.73   10.631%   $199.9434   $199.94   $199.95   $199.90  
  Purchase #2 $149.57   12.449%   $168.19   $168.19   $168.20   $168.20  
  Purchase #3 $240.67   8.538%   $261.2184   $261.22   $261.20   $261.20  
  Purchase #4 $173.26   4.871%   $181.6995   $181.70   $181.70   $181.70  
  Purchase #5 $151.52   13.526%   $172.0146   $172.01   $172.00   $172.00  
  Purchase #6 $205.40   12.777%   $231.644   $231.64   $231.65   $231.60  
  Purchase #7 $65.89   13.795%   $74.9795   $74.98   $75.00   $75.00  
  7 purchase totals = $1,167.04       $1,289.6894   $1,289.68   $1,289.70   $1,289.60