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 $61.92   8.870%   $67.4123   $67.41   $67.40   $67.40  
  Purchase #2 $237.29   13.759%   $269.9387   $269.94   $269.95   $269.90  
  Purchase #3 $35.26   6.348%   $37.4983   $37.50   $37.50   $37.50  
  Purchase #4 $227.41   10.542%   $251.3836   $251.38   $251.40   $251.40  
  Purchase #5 $36.35   3.818%   $37.7378   $37.74   $37.75   $37.70  
  Purchase #6 $246.35   10.759%   $272.8548   $272.85   $272.85   $272.90  
  Purchase #7 $107.46   13.867%   $122.3615   $122.36   $122.35   $122.40  
  7 purchase totals = $952.04       $1,059.1870   $1,059.18   $1,059.20   $1,059.20