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 $91.83   4.135%   $95.6272   $95.63   $95.65   $95.60  
  Purchase #2 $164.28   7.761%   $177.0298   $177.03   $177.05   $177.00  
  Purchase #3 $92.25   7.230%   $98.9197   $98.92   $98.90   $98.90  
  Purchase #4 $106.86   13.177%   $120.9409   $120.94   $120.95   $120.90  
  Purchase #5 $61.63   3.410%   $63.7316   $63.73   $63.75   $63.70  
  Purchase #6 $167.33   7.362%   $179.6488   $179.65   $179.65   $179.60  
  Purchase #7 $41.57   7.342%   $44.6221   $44.62   $44.60   $44.60  
  7 purchase totals = $725.75       $780.5201   $780.52   $780.55   $780.30