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 $185.45   11.642%   $207.0401   $207.04   $207.05   $207.00  
  Purchase #2 $54.45   12.320%   $61.1582   $61.16   $61.15   $61.20  
  Purchase #3 $151.83   6.654%   $161.9328   $161.93   $161.95   $161.90  
  Purchase #4 $186.48   10.115%   $205.3425   $205.34   $205.35   $205.30  
  Purchase #5 $40.98   11.383%   $45.6448   $45.64   $45.65   $45.60  
  Purchase #6 $139.35   6.654%   $148.6223   $148.62   $148.60   $148.60  
  Purchase #7 $126.72   6.221%   $134.6033   $134.60   $134.60   $134.60  
  7 purchase totals = $885.26       $964.3440   $964.33   $964.35   $964.20