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 $244.41   7.337%   $262.3424   $262.34   $262.35   $262.30  
  Purchase #2 $61.40   8.381%   $66.5459   $66.55   $66.55   $66.50  
  Purchase #3 $102.89   3.798%   $106.7978   $106.80   $106.80   $106.80  
  Purchase #4 $212.40   6.143%   $225.4477   $225.45   $225.45   $225.40  
  Purchase #5 $8.75   3.375%   $9.0453   $9.05   $9.05   $9.00  
  Purchase #6 $119.56   12.684%   $134.725   $134.73   $134.75   $134.70  
  Purchase #7 $21.33   6.812%   $22.783   $22.78   $22.80   $22.80  
  7 purchase totals = $770.74       $827.6871   $827.70   $827.75   $827.50