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 $204.69   10.205%   $225.5786   $225.58   $225.60   $225.60  
  Purchase #2 $111.46   9.202%   $121.7165   $121.72   $121.70   $121.70  
  Purchase #3 $237.75   6.429%   $253.0349   $253.03   $253.05   $253.00  
  Purchase #4 $208.55   12.688%   $235.0108   $235.01   $235.00   $235.00  
  Purchase #5 $86.49   11.668%   $96.5817   $96.58   $96.60   $96.60  
  Purchase #6 $173.99   10.328%   $191.9597   $191.96   $191.95   $192.00  
  Purchase #7 $69.62   5.248%   $73.2737   $73.27   $73.25   $73.30  
  7 purchase totals = $1,092.55       $1,197.1559   $1,197.15   $1,197.15   $1,197.20