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 $128.51   7.113%   $137.6509   $137.65   $137.65   $137.70  
  Purchase #2 $65.77   4.160%   $68.506   $68.51   $68.50   $68.50  
  Purchase #3 $113.31   4.768%   $118.7126   $118.71   $118.70   $118.70  
  Purchase #4 $55.46   10.663%   $61.3737   $61.37   $61.35   $61.40  
  Purchase #5 $225.94   3.734%   $234.3766   $234.38   $234.40   $234.40  
  Purchase #6 $238.47   9.797%   $261.8329   $261.83   $261.85   $261.80  
  Purchase #7 $153.55   5.296%   $161.682   $161.68   $161.70   $161.70  
  7 purchase totals = $981.01       $1,044.1347   $1,044.13   $1,044.15   $1,044.20