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 $195.63   6.326%   $208.0056   $208.01   $208.00   $208.00  
  Purchase #2 $217.34   8.566%   $235.9573   $235.96   $235.95   $236.00  
  Purchase #3 $155.77   6.617%   $166.0773   $166.08   $166.10   $166.10  
  Purchase #4 $58.67   3.259%   $60.5821   $60.58   $60.60   $60.60  
  Purchase #5 $212.29   5.294%   $223.5286   $223.53   $223.55   $223.50  
  Purchase #6 $244.67   5.721%   $258.6676   $258.67   $258.65   $258.70  
  Purchase #7 $230.99   6.431%   $245.845   $245.85   $245.85   $245.80  
  7 purchase totals = $1,315.36       $1,398.6635   $1,398.68   $1,398.70   $1,398.70