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 $244.66   7.436%   $262.8529   $262.85   $262.85   $262.90  
  Purchase #2 $130.71   11.466%   $145.6972   $145.70   $145.70   $145.70  
  Purchase #3 $66.48   11.201%   $73.9264   $73.93   $73.95   $73.90  
  Purchase #4 $225.78   9.249%   $246.6624   $246.66   $246.65   $246.70  
  Purchase #5 $134.40   4.129%   $139.9494   $139.95   $139.95   $139.90  
  Purchase #6 $154.28   11.455%   $171.9528   $171.95   $171.95   $172.00  
  Purchase #7 $7.77   12.310%   $8.7265   $8.73   $8.75   $8.70  
  7 purchase totals = $964.08       $1,049.7676   $1,049.77   $1,049.80   $1,049.80