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 $182.83   13.818%   $208.0934   $208.09   $208.10   $208.10  
  Purchase #2 $61.59   12.287%   $69.1576   $69.16   $69.15   $69.20  
  Purchase #3 $141.34   4.278%   $147.3865   $147.39   $147.40   $147.40  
  Purchase #4 $68.32   3.516%   $70.7221   $70.72   $70.70   $70.70  
  Purchase #5 $191.35   7.433%   $205.573   $205.57   $205.55   $205.60  
  Purchase #6 $225.89   11.522%   $251.917   $251.92   $251.90   $251.90  
  Purchase #7 $44.36   7.590%   $47.7269   $47.73   $47.75   $47.70  
  7 purchase totals = $915.68       $1,000.5765   $1,000.58   $1,000.55   $1,000.60