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 $208.64   4.713%   $218.4732   $218.47   $218.45   $218.50  
  Purchase #2 $181.87   8.498%   $197.3253   $197.33   $197.35   $197.30  
  Purchase #3 $158.78   7.749%   $171.0839   $171.08   $171.10   $171.10  
  Purchase #4 $80.79   7.151%   $86.5673   $86.57   $86.55   $86.60  
  Purchase #5 $157.85   6.732%   $168.4765   $168.48   $168.50   $168.50  
  Purchase #6 $204.61   10.784%   $226.6751   $226.68   $226.70   $226.70  
  Purchase #7 $85.62   7.559%   $92.092   $92.09   $92.10   $92.10  
  7 purchase totals = $1,078.16       $1,160.6933   $1,160.70   $1,160.75   $1,160.80