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 $167.82   10.320%   $185.139   $185.14   $185.15   $185.10  
  Purchase #2 $204.26   11.451%   $227.6498   $227.65   $227.65   $227.60  
  Purchase #3 $159.60   6.821%   $170.4863   $170.49   $170.50   $170.50  
  Purchase #4 $64.30   11.134%   $71.4592   $71.46   $71.45   $71.50  
  Purchase #5 $170.30   12.651%   $191.8447   $191.84   $191.85   $191.80  
  Purchase #6 $51.36   4.599%   $53.722   $53.72   $53.70   $53.70  
  Purchase #7 $174.40   13.269%   $197.5411   $197.54   $197.55   $197.50  
  7 purchase totals = $992.04       $1,097.8421   $1,097.84   $1,097.85   $1,097.70