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 $109.67   3.210%   $113.1904   $113.19   $113.20   $113.20  
  Purchase #2 $231.91   13.845%   $264.0179   $264.02   $264.00   $264.00  
  Purchase #3 $39.39   7.861%   $42.4864   $42.49   $42.50   $42.50  
  Purchase #4 $208.68   3.779%   $216.566   $216.57   $216.55   $216.60  
  Purchase #5 $103.78   12.307%   $116.5522   $116.55   $116.55   $116.60  
  Purchase #6 $242.67   4.523%   $253.646   $253.65   $253.65   $253.60  
  Purchase #7 $146.32   5.341%   $154.135   $154.14   $154.15   $154.10  
  7 purchase totals = $1,082.42       $1,160.5939   $1,160.61   $1,160.60   $1,160.60