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 $184.77   12.215%   $207.3397   $207.34   $207.35   $207.30  
  Purchase #2 $168.83   12.755%   $190.3643   $190.36   $190.35   $190.40  
  Purchase #3 $70.27   7.523%   $75.5564   $75.56   $75.55   $75.60  
  Purchase #4 $83.87   10.633%   $92.7879   $92.79   $92.80   $92.80  
  Purchase #5 $116.41   7.218%   $124.8125   $124.81   $124.80   $124.80  
  Purchase #6 $127.46   12.500%   $143.3925   $143.39   $143.40   $143.40  
  Purchase #7 $171.76   11.340%   $191.2376   $191.24   $191.25   $191.20  
  7 purchase totals = $923.37       $1,025.4909   $1,025.49   $1,025.50   $1,025.50