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 $58.84   3.607%   $60.9624   $60.96   $60.95   $61.00  
  Purchase #2 $13.97   5.655%   $14.76   $14.76   $14.75   $14.80  
  Purchase #3 $112.58   4.615%   $117.7756   $117.78   $117.80   $117.80  
  Purchase #4 $98.87   9.238%   $108.0036   $108.00   $108.00   $108.00  
  Purchase #5 $190.46   5.189%   $200.343   $200.34   $200.35   $200.30  
  Purchase #6 $67.66   10.419%   $74.7095   $74.71   $74.70   $74.70  
  Purchase #7 $68.78   6.476%   $73.2342   $73.23   $73.25   $73.20  
  7 purchase totals = $611.16       $649.7883   $649.78   $649.80   $649.80