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 $14.96   8.609%   $16.2479   $16.25   $16.25   $16.20  
  Purchase #2 $113.35   10.335%   $125.0647   $125.06   $125.05   $125.10  
  Purchase #3 $223.59   6.179%   $237.4056   $237.41   $237.40   $237.40  
  Purchase #4 $90.91   9.527%   $99.571   $99.57   $99.55   $99.60  
  Purchase #5 $26.69   4.325%   $27.8443   $27.84   $27.85   $27.80  
  Purchase #6 $62.43   8.616%   $67.809   $67.81   $67.80   $67.80  
  Purchase #7 $171.39   6.352%   $182.2767   $182.28   $182.30   $182.30  
  7 purchase totals = $703.32       $756.2192   $756.22   $756.20   $756.20