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 $207.98   8.801%   $226.2843   $226.28   $226.30   $226.30  
  Purchase #2 $131.49   12.431%   $147.8355   $147.84   $147.85   $147.80  
  Purchase #3 $78.43   5.377%   $82.6472   $82.65   $82.65   $82.60  
  Purchase #4 $167.50   12.299%   $188.1008   $188.10   $188.10   $188.10  
  Purchase #5 $244.88   13.271%   $277.378   $277.38   $277.40   $277.40  
  Purchase #6 $184.31   5.734%   $194.8783   $194.88   $194.90   $194.90  
  Purchase #7 $78.74   4.426%   $82.225   $82.23   $82.25   $82.20  
  7 purchase totals = $1,093.33       $1,199.3491   $1,199.36   $1,199.45   $1,199.30