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 $93.63   4.816%   $98.1392   $98.14   $98.15   $98.10  
  Purchase #2 $61.81   5.874%   $65.4407   $65.44   $65.45   $65.40  
  Purchase #3 $224.56   12.103%   $251.7385   $251.74   $251.75   $251.70  
  Purchase #4 $194.96   4.833%   $204.3824   $204.38   $204.40   $204.40  
  Purchase #5 $64.66   7.802%   $69.7048   $69.70   $69.70   $69.70  
  Purchase #6 $216.75   13.316%   $245.6124   $245.61   $245.60   $245.60  
  Purchase #7 $194.83   3.417%   $201.4873   $201.49   $201.50   $201.50  
  7 purchase totals = $1,051.20       $1,136.5053   $1,136.50   $1,136.55   $1,136.40