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 $216.29   6.802%   $231.002   $231.00   $231.00   $231.00  
  Purchase #2 $11.37   13.449%   $12.8992   $12.90   $12.90   $12.90  
  Purchase #3 $172.81   8.522%   $187.5369   $187.54   $187.55   $187.50  
  Purchase #4 $22.88   4.735%   $23.9634   $23.96   $23.95   $24.00  
  Purchase #5 $136.45   12.516%   $153.5281   $153.53   $153.55   $153.50  
  Purchase #6 $177.57   6.172%   $188.5296   $188.53   $188.55   $188.50  
  Purchase #7 $60.80   5.627%   $64.2212   $64.22   $64.20   $64.20  
  7 purchase totals = $798.17       $861.6804   $861.68   $861.70   $861.60