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 $36.60   12.122%   $41.0367   $41.04   $41.05   $41.00  
  Purchase #2 $46.84   10.264%   $51.6477   $51.65   $51.65   $51.60  
  Purchase #3 $155.78   13.589%   $176.9489   $176.95   $176.95   $176.90  
  Purchase #4 $214.38   5.380%   $225.9136   $225.91   $225.90   $225.90  
  Purchase #5 $81.75   5.585%   $86.3157   $86.32   $86.30   $86.30  
  Purchase #6 $37.40   12.269%   $41.9886   $41.99   $42.00   $42.00  
  Purchase #7 $124.50   11.532%   $138.8573   $138.86   $138.85   $138.90  
  7 purchase totals = $697.25       $762.7085   $762.72   $762.70   $762.60