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 $220.57   11.557%   $246.0613   $246.06   $246.05   $246.10  
  Purchase #2 $128.25   4.717%   $134.2996   $134.30   $134.30   $134.30  
  Purchase #3 $119.98   6.745%   $128.0727   $128.07   $128.05   $128.10  
  Purchase #4 $87.64   11.360%   $97.5959   $97.60   $97.60   $97.60  
  Purchase #5 $22.95   6.209%   $24.375   $24.38   $24.40   $24.40  
  Purchase #6 $15.54   3.859%   $16.1397   $16.14   $16.15   $16.10  
  Purchase #7 $194.33   6.522%   $207.0042   $207.00   $207.00   $207.00  
  7 purchase totals = $789.26       $853.5484   $853.55   $853.55   $853.60