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 $84.64   9.273%   $92.4887   $92.49   $92.50   $92.50  
  Purchase #2 $34.99   8.164%   $37.8466   $37.85   $37.85   $37.80  
  Purchase #3 $169.78   7.560%   $182.6154   $182.62   $182.60   $182.60  
  Purchase #4 $26.92   13.459%   $30.5432   $30.54   $30.55   $30.50  
  Purchase #5 $165.68   11.863%   $185.3346   $185.33   $185.35   $185.30  
  Purchase #6 $83.88   10.787%   $92.9281   $92.93   $92.95   $92.90  
  Purchase #7 $246.29   10.441%   $272.0051   $272.01   $272.00   $272.00  
  7 purchase totals = $812.18       $893.7617   $893.77   $893.80   $893.60