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 $217.51   10.483%   $240.3116   $240.31   $240.30   $240.30  
  Purchase #2 $152.91   8.556%   $165.993   $165.99   $166.00   $166.00  
  Purchase #3 $130.68   9.188%   $142.6869   $142.69   $142.70   $142.70  
  Purchase #4 $42.84   8.639%   $46.5409   $46.54   $46.55   $46.50  
  Purchase #5 $218.69   7.801%   $235.75   $235.75   $235.75   $235.80  
  Purchase #6 $41.75   11.285%   $46.4615   $46.46   $46.45   $46.50  
  Purchase #7 $238.92   12.568%   $268.9475   $268.95   $268.95   $268.90  
  7 purchase totals = $1,043.30       $1,146.6914   $1,146.69   $1,146.70   $1,146.70