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 $236.69   13.593%   $268.8633   $268.86   $268.85   $268.90  
  Purchase #2 $193.69   4.643%   $202.683   $202.68   $202.70   $202.70  
  Purchase #3 $51.78   9.655%   $56.7794   $56.78   $56.80   $56.80  
  Purchase #4 $220.47   12.236%   $247.4467   $247.45   $247.45   $247.40  
  Purchase #5 $60.75   5.843%   $64.2996   $64.30   $64.30   $64.30  
  Purchase #6 $242.92   6.218%   $258.0248   $258.02   $258.00   $258.00  
  Purchase #7 $238.83   3.815%   $247.9414   $247.94   $247.95   $247.90  
  7 purchase totals = $1,245.13       $1,346.0382   $1,346.03   $1,346.05   $1,346.00