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 $124.91   13.424%   $141.6779   $141.68   $141.70   $141.70  
  Purchase #2 $228.64   4.617%   $239.1963   $239.20   $239.20   $239.20  
  Purchase #3 $43.94   8.780%   $47.7979   $47.80   $47.80   $47.80  
  Purchase #4 $52.92   4.842%   $55.4824   $55.48   $55.50   $55.50  
  Purchase #5 $221.60   5.171%   $233.0589   $233.06   $233.05   $233.10  
  Purchase #6 $188.59   5.494%   $198.9511   $198.95   $198.95   $199.00  
  Purchase #7 $110.90   7.676%   $119.4127   $119.41   $119.40   $119.40  
  7 purchase totals = $971.50       $1,035.5772   $1,035.58   $1,035.60   $1,035.70