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 $18.38   5.340%   $19.3615   $19.36   $19.35   $19.40  
  Purchase #2 $84.64   12.861%   $95.5256   $95.53   $95.55   $95.50  
  Purchase #3 $48.94   8.867%   $53.2795   $53.28   $53.30   $53.30  
  Purchase #4 $16.81   6.669%   $17.9311   $17.93   $17.95   $17.90  
  Purchase #5 $91.32   5.184%   $96.054   $96.05   $96.05   $96.10  
  Purchase #6 $186.99   7.814%   $201.6014   $201.60   $201.60   $201.60  
  Purchase #7 $233.39   5.327%   $245.8227   $245.82   $245.80   $245.80  
  7 purchase totals = $680.47       $729.5758   $729.57   $729.60   $729.60