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 $211.59   6.227%   $224.7657   $224.77   $224.75   $224.80  
  Purchase #2 $94.78   12.405%   $106.5375   $106.54   $106.55   $106.50  
  Purchase #3 $16.28   11.133%   $18.0925   $18.09   $18.10   $18.10  
  Purchase #4 $109.49   3.769%   $113.6167   $113.62   $113.60   $113.60  
  Purchase #5 $119.54   10.486%   $132.075   $132.08   $132.10   $132.10  
  Purchase #6 $144.33   5.330%   $152.0228   $152.02   $152.00   $152.00  
  Purchase #7 $27.62   11.361%   $30.7579   $30.76   $30.75   $30.80  
  7 purchase totals = $723.63       $777.8681   $777.88   $777.85   $777.90