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 $70.98   8.406%   $76.9466   $76.95   $76.95   $76.90  
  Purchase #2 $10.84   6.653%   $11.5612   $11.56   $11.55   $11.60  
  Purchase #3 $154.69   10.363%   $170.7205   $170.72   $170.70   $170.70  
  Purchase #4 $144.58   10.607%   $159.9156   $159.92   $159.90   $159.90  
  Purchase #5 $168.58   3.544%   $174.5545   $174.55   $174.55   $174.60  
  Purchase #6 $238.40   8.869%   $259.5437   $259.54   $259.55   $259.50  
  Purchase #7 $33.56   4.202%   $34.9702   $34.97   $34.95   $35.00  
  7 purchase totals = $821.63       $888.2123   $888.21   $888.15   $888.20