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 $153.46   8.766%   $166.9123   $166.91   $166.90   $166.90  
  Purchase #2 $244.57   7.617%   $263.1989   $263.20   $263.20   $263.20  
  Purchase #3 $163.86   8.347%   $177.5374   $177.54   $177.55   $177.50  
  Purchase #4 $56.41   13.325%   $63.9266   $63.93   $63.95   $63.90  
  Purchase #5 $78.50   12.787%   $88.5378   $88.54   $88.55   $88.50  
  Purchase #6 $150.85   3.428%   $156.0211   $156.02   $156.00   $156.00  
  Purchase #7 $111.69   9.594%   $122.4055   $122.41   $122.40   $122.40  
  7 purchase totals = $959.34       $1,038.5396   $1,038.55   $1,038.55   $1,038.40