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 $62.52   13.702%   $71.0865   $71.09   $71.10   $71.10  
  Purchase #2 $132.80   8.337%   $143.8715   $143.87   $143.85   $143.90  
  Purchase #3 $22.73   4.264%   $23.6992   $23.70   $23.70   $23.70  
  Purchase #4 $232.37   13.813%   $264.4673   $264.47   $264.45   $264.50  
  Purchase #5 $204.28   13.351%   $231.5534   $231.55   $231.55   $231.60  
  Purchase #6 $14.34   3.389%   $14.826   $14.83   $14.85   $14.80  
  Purchase #7 $162.95   4.372%   $170.0742   $170.07   $170.05   $170.10  
  7 purchase totals = $831.99       $919.5781   $919.58   $919.55   $919.70