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 $208.99   10.783%   $231.5254   $231.53   $231.55   $231.50  
  Purchase #2 $223.55   5.811%   $236.5405   $236.54   $236.55   $236.50  
  Purchase #3 $32.70   3.572%   $33.868   $33.87   $33.85   $33.90  
  Purchase #4 $247.90   9.229%   $270.7787   $270.78   $270.80   $270.80  
  Purchase #5 $223.29   12.866%   $252.0185   $252.02   $252.00   $252.00  
  Purchase #6 $202.96   6.816%   $216.7938   $216.79   $216.80   $216.80  
  Purchase #7 $74.64   13.835%   $84.9664   $84.97   $84.95   $85.00  
  7 purchase totals = $1,214.03       $1,326.4913   $1,326.50   $1,326.50   $1,326.50