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 $181.45   7.528%   $195.1096   $195.11   $195.10   $195.10  
  Purchase #2 $128.39   5.798%   $135.8341   $135.83   $135.85   $135.80  
  Purchase #3 $32.64   11.530%   $36.4034   $36.40   $36.40   $36.40  
  Purchase #4 $113.83   8.110%   $123.0616   $123.06   $123.05   $123.10  
  Purchase #5 $27.44   11.425%   $30.575   $30.58   $30.60   $30.60  
  Purchase #6 $186.71   12.567%   $210.1738   $210.17   $210.15   $210.20  
  Purchase #7 $38.85   9.753%   $42.639   $42.64   $42.65   $42.60  
  7 purchase totals = $709.31       $773.7965   $773.79   $773.80   $773.80