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 $31.41   11.553%   $35.0388   $35.04   $35.05   $35.00  
  Purchase #2 $103.42   4.308%   $107.8753   $107.88   $107.90   $107.90  
  Purchase #3 $221.95   13.639%   $252.2218   $252.22   $252.20   $252.20  
  Purchase #4 $212.88   13.775%   $242.2042   $242.20   $242.20   $242.20  
  Purchase #5 $246.40   4.627%   $257.8009   $257.80   $257.80   $257.80  
  Purchase #6 $183.38   11.117%   $203.7664   $203.77   $203.75   $203.80  
  Purchase #7 $165.53   6.357%   $176.0527   $176.05   $176.05   $176.10  
  7 purchase totals = $1,164.97       $1,274.9601   $1,274.96   $1,274.95   $1,275.00