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 $192.54   13.395%   $218.3307   $218.33   $218.35   $218.30  
  Purchase #2 $65.55   10.318%   $72.3134   $72.31   $72.30   $72.30  
  Purchase #3 $59.78   7.107%   $64.0286   $64.03   $64.05   $64.00  
  Purchase #4 $155.53   7.388%   $167.0206   $167.02   $167.00   $167.00  
  Purchase #5 $121.69   12.569%   $136.9852   $136.99   $137.00   $137.00  
  Purchase #6 $247.33   4.311%   $257.9924   $257.99   $258.00   $258.00  
  Purchase #7 $94.39   13.453%   $107.0883   $107.09   $107.10   $107.10  
  7 purchase totals = $936.81       $1,023.7592   $1,023.76   $1,023.80   $1,023.70