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 $230.50   13.693%   $262.0624   $262.06   $262.05   $262.10  
  Purchase #2 $217.39   8.562%   $236.0029   $236.00   $236.00   $236.00  
  Purchase #3 $123.82   11.255%   $137.7559   $137.76   $137.75   $137.80  
  Purchase #4 $18.55   11.815%   $20.7417   $20.74   $20.75   $20.70  
  Purchase #5 $206.99   9.605%   $226.8714   $226.87   $226.85   $226.90  
  Purchase #6 $49.71   4.807%   $52.0996   $52.10   $52.10   $52.10  
  Purchase #7 $73.74   9.119%   $80.4644   $80.46   $80.45   $80.50  
  7 purchase totals = $920.70       $1,015.9983   $1,015.99   $1,015.95   $1,016.10