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 $161.38   3.854%   $167.5996   $167.60   $167.60   $167.60  
  Purchase #2 $239.78   6.218%   $254.6895   $254.69   $254.70   $254.70  
  Purchase #3 $95.48   6.629%   $101.8094   $101.81   $101.80   $101.80  
  Purchase #4 $164.26   12.298%   $184.4607   $184.46   $184.45   $184.50  
  Purchase #5 $245.75   11.436%   $273.854   $273.85   $273.85   $273.90  
  Purchase #6 $137.95   10.205%   $152.0278   $152.03   $152.05   $152.00  
  Purchase #7 $217.36   12.422%   $244.3605   $244.36   $244.35   $244.40  
  7 purchase totals = $1,261.96       $1,378.8015   $1,378.80   $1,378.80   $1,378.90