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 $63.63   3.786%   $66.039   $66.04   $66.05   $66.00  
  Purchase #2 $214.98   9.787%   $236.0201   $236.02   $236.00   $236.00  
  Purchase #3 $174.57   10.672%   $193.2001   $193.20   $193.20   $193.20  
  Purchase #4 $87.38   10.683%   $96.7148   $96.71   $96.70   $96.70  
  Purchase #5 $243.99   3.528%   $252.598   $252.60   $252.60   $252.60  
  Purchase #6 $49.51   11.347%   $55.1279   $55.13   $55.15   $55.10  
  Purchase #7 $190.35   6.675%   $203.0559   $203.06   $203.05   $203.10  
  7 purchase totals = $1,024.41       $1,102.7558   $1,102.76   $1,102.75   $1,102.70