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 $83.58   10.721%   $92.5406   $92.54   $92.55   $92.50  
  Purchase #2 $180.91   3.226%   $186.7462   $186.75   $186.75   $186.70  
  Purchase #3 $176.58   6.201%   $187.5297   $187.53   $187.55   $187.50  
  Purchase #4 $39.71   7.309%   $42.6124   $42.61   $42.60   $42.60  
  Purchase #5 $142.38   8.626%   $154.6617   $154.66   $154.65   $154.70  
  Purchase #6 $134.49   8.516%   $145.9432   $145.94   $145.95   $145.90  
  Purchase #7 $14.53   6.795%   $15.5173   $15.52   $15.50   $15.50  
  7 purchase totals = $772.18       $825.5511   $825.55   $825.55   $825.40