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 $218.98   12.762%   $246.9262   $246.93   $246.95   $246.90  
  Purchase #2 $185.58   10.134%   $204.3867   $204.39   $204.40   $204.40  
  Purchase #3 $243.45   8.762%   $264.7811   $264.78   $264.80   $264.80  
  Purchase #4 $196.30   5.824%   $207.7325   $207.73   $207.75   $207.70  
  Purchase #5 $62.62   11.458%   $69.795   $69.80   $69.80   $69.80  
  Purchase #6 $224.37   4.147%   $233.6746   $233.67   $233.65   $233.70  
  Purchase #7 $16.45   12.471%   $18.5015   $18.50   $18.50   $18.50  
  7 purchase totals = $1,147.75       $1,245.7976   $1,245.80   $1,245.85   $1,245.80