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 $171.73   12.212%   $192.7017   $192.70   $192.70   $192.70  
  Purchase #2 $103.76   5.432%   $109.3962   $109.40   $109.40   $109.40  
  Purchase #3 $201.97   6.481%   $215.0597   $215.06   $215.05   $215.10  
  Purchase #4 $206.25   7.453%   $221.6218   $221.62   $221.60   $221.60  
  Purchase #5 $165.42   5.758%   $174.9449   $174.94   $174.95   $174.90  
  Purchase #6 $131.34   12.286%   $147.4764   $147.48   $147.50   $147.50  
  Purchase #7 $218.53   9.151%   $238.5277   $238.53   $238.55   $238.50  
  7 purchase totals = $1,199.00       $1,299.7284   $1,299.73   $1,299.75   $1,299.70