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 $85.54   8.416%   $92.739   $92.74   $92.75   $92.70  
  Purchase #2 $179.42   3.691%   $186.0424   $186.04   $186.05   $186.00  
  Purchase #3 $206.66   6.314%   $219.7085   $219.71   $219.70   $219.70  
  Purchase #4 $12.47   6.144%   $13.2362   $13.24   $13.25   $13.20  
  Purchase #5 $184.98   4.507%   $193.317   $193.32   $193.30   $193.30  
  Purchase #6 $192.59   4.242%   $200.7597   $200.76   $200.75   $200.80  
  Purchase #7 $22.81   5.448%   $24.0527   $24.05   $24.05   $24.10  
  7 purchase totals = $884.47       $929.8555   $929.86   $929.85   $929.80