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 $53.97   10.526%   $59.6509   $59.65   $59.65   $59.70  
  Purchase #2 $84.77   11.585%   $94.5906   $94.59   $94.60   $94.60  
  Purchase #3 $139.27   5.577%   $147.0371   $147.04   $147.05   $147.00  
  Purchase #4 $11.26   3.454%   $11.6489   $11.65   $11.65   $11.60  
  Purchase #5 $117.43   4.385%   $122.5793   $122.58   $122.60   $122.60  
  Purchase #6 $49.80   11.390%   $55.4722   $55.47   $55.45   $55.50  
  Purchase #7 $108.48   9.665%   $118.9646   $118.96   $118.95   $119.00  
  7 purchase totals = $564.98       $609.9436   $609.94   $609.95   $610.00