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 $192.26   8.327%   $208.2695   $208.27   $208.25   $208.30  
  Purchase #2 $177.83   7.267%   $190.7529   $190.75   $190.75   $190.80  
  Purchase #3 $17.52   12.746%   $19.7531   $19.75   $19.75   $19.80  
  Purchase #4 $199.81   8.380%   $216.5541   $216.55   $216.55   $216.60  
  Purchase #5 $120.87   11.778%   $135.1061   $135.11   $135.10   $135.10  
  Purchase #6 $23.37   9.858%   $25.6738   $25.67   $25.65   $25.70  
  Purchase #7 $199.78   3.565%   $206.9022   $206.90   $206.90   $206.90  
  7 purchase totals = $931.44       $1,003.0117   $1,003.00   $1,002.95   $1,003.20