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 $90.50   12.638%   $101.9374   $101.94   $101.95   $101.90  
  Purchase #2 $239.26   7.568%   $257.3672   $257.37   $257.35   $257.40  
  Purchase #3 $195.41   4.181%   $203.5801   $203.58   $203.60   $203.60  
  Purchase #4 $68.69   8.516%   $74.5396   $74.54   $74.55   $74.50  
  Purchase #5 $232.58   10.106%   $256.0845   $256.08   $256.10   $256.10  
  Purchase #6 $60.54   9.330%   $66.1884   $66.19   $66.20   $66.20  
  Purchase #7 $215.66   9.850%   $236.9025   $236.90   $236.90   $236.90  
  7 purchase totals = $1,102.64       $1,196.5997   $1,196.60   $1,196.65   $1,196.60