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 $66.85   13.559%   $75.9142   $75.91   $75.90   $75.90  
  Purchase #2 $144.96   5.492%   $152.9212   $152.92   $152.90   $152.90  
  Purchase #3 $250.54   10.107%   $275.8621   $275.86   $275.85   $275.90  
  Purchase #4 $237.49   8.440%   $257.5342   $257.53   $257.55   $257.50  
  Purchase #5 $41.59   13.483%   $47.1976   $47.20   $47.20   $47.20  
  Purchase #6 $63.60   6.847%   $67.9547   $67.95   $67.95   $68.00  
  Purchase #7 $140.94   7.868%   $152.0292   $152.03   $152.05   $152.00  
  7 purchase totals = $945.97       $1,029.4132   $1,029.40   $1,029.40   $1,029.40