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 $171.67   8.782%   $186.7461   $186.75   $186.75   $186.70  
  Purchase #2 $235.87   12.692%   $265.8066   $265.81   $265.80   $265.80  
  Purchase #3 $31.81   13.256%   $36.0267   $36.03   $36.05   $36.00  
  Purchase #4 $52.96   4.828%   $55.5169   $55.52   $55.50   $55.50  
  Purchase #5 $132.62   7.379%   $142.406   $142.41   $142.40   $142.40  
  Purchase #6 $121.73   13.160%   $137.7497   $137.75   $137.75   $137.70  
  Purchase #7 $247.74   5.712%   $261.8909   $261.89   $261.90   $261.90  
  7 purchase totals = $994.40       $1,086.1429   $1,086.16   $1,086.15   $1,086.00