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 $166.61   10.296%   $183.7642   $183.76   $183.75   $183.80  
  Purchase #2 $152.55   6.342%   $162.2247   $162.22   $162.20   $162.20  
  Purchase #3 $190.60   5.573%   $201.2221   $201.22   $201.20   $201.20  
  Purchase #4 $134.81   10.117%   $148.4487   $148.45   $148.45   $148.40  
  Purchase #5 $136.78   11.627%   $152.6834   $152.68   $152.70   $152.70  
  Purchase #6 $161.93   13.554%   $183.878   $183.88   $183.90   $183.90  
  Purchase #7 $133.58   7.186%   $143.1791   $143.18   $143.20   $143.20  
  7 purchase totals = $1,076.86       $1,175.4002   $1,175.39   $1,175.40   $1,175.40