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 $55.85   9.692%   $61.263   $61.26   $61.25   $61.30  
  Purchase #2 $63.38   10.167%   $69.8238   $69.82   $69.80   $69.80  
  Purchase #3 $100.25   13.477%   $113.7607   $113.76   $113.75   $113.80  
  Purchase #4 $60.64   4.486%   $63.3603   $63.36   $63.35   $63.40  
  Purchase #5 $241.86   13.833%   $275.3165   $275.32   $275.30   $275.30  
  Purchase #6 $143.33   5.108%   $150.6513   $150.65   $150.65   $150.70  
  Purchase #7 $193.46   11.629%   $215.9575   $215.96   $215.95   $216.00  
  7 purchase totals = $858.77       $950.1331   $950.13   $950.05   $950.30