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 $188.86   13.608%   $214.5601   $214.56   $214.55   $214.60  
  Purchase #2 $140.33   8.772%   $152.6397   $152.64   $152.65   $152.60  
  Purchase #3 $132.50   11.301%   $147.4738   $147.47   $147.45   $147.50  
  Purchase #4 $37.31   10.140%   $41.0932   $41.09   $41.10   $41.10  
  Purchase #5 $186.87   4.715%   $195.6809   $195.68   $195.70   $195.70  
  Purchase #6 $216.65   11.727%   $242.0565   $242.06   $242.05   $242.10  
  Purchase #7 $8.42   12.769%   $9.4951   $9.50   $9.50   $9.50  
  7 purchase totals = $910.94       $1,002.9993   $1,003.00   $1,003.00   $1,003.10