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 $245.65   6.545%   $261.7278   $261.73   $261.75   $261.70  
  Purchase #2 $51.81   7.229%   $55.5553   $55.56   $55.55   $55.60  
  Purchase #3 $18.66   4.745%   $19.5454   $19.55   $19.55   $19.50  
  Purchase #4 $219.96   10.705%   $243.5067   $243.51   $243.50   $243.50  
  Purchase #5 $152.45   6.762%   $162.7587   $162.76   $162.75   $162.80  
  Purchase #6 $216.94   12.477%   $244.0076   $244.01   $244.00   $244.00  
  Purchase #7 $13.83   6.169%   $14.6832   $14.68   $14.70   $14.70  
  7 purchase totals = $919.30       $1,001.7847   $1,001.80   $1,001.80   $1,001.80