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 $119.89   3.263%   $123.802   $123.80   $123.80   $123.80  
  Purchase #2 $188.34   7.653%   $202.7537   $202.75   $202.75   $202.80  
  Purchase #3 $154.59   6.439%   $164.5441   $164.54   $164.55   $164.50  
  Purchase #4 $95.75   10.675%   $105.9713   $105.97   $105.95   $106.00  
  Purchase #5 $182.28   5.726%   $192.7174   $192.72   $192.70   $192.70  
  Purchase #6 $5.46   9.789%   $5.9945   $5.99   $6.00   $6.00  
  Purchase #7 $22.37   6.187%   $23.754   $23.75   $23.75   $23.80  
  7 purchase totals = $768.68       $819.5370   $819.52   $819.50   $819.60