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 $200.43   10.392%   $221.2587   $221.26   $221.25   $221.30  
  Purchase #2 $113.26   8.801%   $123.228   $123.23   $123.25   $123.20  
  Purchase #3 $11.66   5.139%   $12.2592   $12.26   $12.25   $12.30  
  Purchase #4 $140.41   3.737%   $145.6571   $145.66   $145.65   $145.70  
  Purchase #5 $152.92   6.858%   $163.4073   $163.41   $163.40   $163.40  
  Purchase #6 $220.91   11.484%   $246.2793   $246.28   $246.30   $246.30  
  Purchase #7 $77.38   7.732%   $83.363   $83.36   $83.35   $83.40  
  7 purchase totals = $916.97       $995.4526   $995.46   $995.45   $995.60