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 $44.82   13.664%   $50.9442   $50.94   $50.95   $50.90  
  Purchase #2 $51.99   3.188%   $53.6474   $53.65   $53.65   $53.60  
  Purchase #3 $132.54   8.417%   $143.6959   $143.70   $143.70   $143.70  
  Purchase #4 $169.72   4.108%   $176.6921   $176.69   $176.70   $176.70  
  Purchase #5 $148.96   10.761%   $164.9896   $164.99   $165.00   $165.00  
  Purchase #6 $24.44   8.708%   $26.5682   $26.57   $26.55   $26.60  
  Purchase #7 $152.85   4.364%   $159.5204   $159.52   $159.50   $159.50  
  7 purchase totals = $725.32       $776.0578   $776.06   $776.05   $776.00