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 $101.34   12.523%   $114.0308   $114.03   $114.05   $114.00  
  Purchase #2 $87.62   9.614%   $96.0438   $96.04   $96.05   $96.00  
  Purchase #3 $57.59   13.872%   $65.5789   $65.58   $65.60   $65.60  
  Purchase #4 $81.38   3.558%   $84.2755   $84.28   $84.30   $84.30  
  Purchase #5 $111.95   6.618%   $119.3589   $119.36   $119.35   $119.40  
  Purchase #6 $147.66   5.500%   $155.7813   $155.78   $155.80   $155.80  
  Purchase #7 $130.42   6.135%   $138.4213   $138.42   $138.40   $138.40  
  7 purchase totals = $717.96       $773.4905   $773.49   $773.55   $773.50