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 $64.32   3.237%   $66.402   $66.40   $66.40   $66.40  
  Purchase #2 $206.49   7.674%   $222.336   $222.34   $222.35   $222.30  
  Purchase #3 $31.34   10.766%   $34.7141   $34.71   $34.70   $34.70  
  Purchase #4 $45.57   5.469%   $48.0622   $48.06   $48.05   $48.10  
  Purchase #5 $205.99   3.383%   $212.9586   $212.96   $212.95   $213.00  
  Purchase #6 $196.35   4.833%   $205.8396   $205.84   $205.85   $205.80  
  Purchase #7 $204.26   10.666%   $226.0464   $226.05   $226.05   $226.00  
  7 purchase totals = $954.32       $1,016.3589   $1,016.36   $1,016.35   $1,016.30