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 $181.76   13.316%   $205.9632   $205.96   $205.95   $206.00  
  Purchase #2 $119.67   5.284%   $125.9934   $125.99   $126.00   $126.00  
  Purchase #3 $90.48   13.109%   $102.341   $102.34   $102.35   $102.30  
  Purchase #4 $42.98   8.420%   $46.5989   $46.60   $46.60   $46.60  
  Purchase #5 $61.71   4.217%   $64.3123   $64.31   $64.30   $64.30  
  Purchase #6 $240.61   7.158%   $257.8329   $257.83   $257.85   $257.80  
  Purchase #7 $224.30   9.774%   $246.2231   $246.22   $246.20   $246.20  
  7 purchase totals = $961.51       $1,049.2648   $1,049.25   $1,049.25   $1,049.20