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 $53.48   3.372%   $55.2833   $55.28   $55.30   $55.30  
  Purchase #2 $249.90   6.117%   $265.1864   $265.19   $265.20   $265.20  
  Purchase #3 $84.67   6.209%   $89.9272   $89.93   $89.95   $89.90  
  Purchase #4 $45.75   12.225%   $51.3429   $51.34   $51.35   $51.30  
  Purchase #5 $154.61   8.311%   $167.4596   $167.46   $167.45   $167.50  
  Purchase #6 $66.87   4.215%   $69.6886   $69.69   $69.70   $69.70  
  Purchase #7 $80.62   9.266%   $88.0902   $88.09   $88.10   $88.10  
  7 purchase totals = $735.90       $786.9782   $786.98   $787.05   $787.00