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 $62.28   5.484%   $65.6954   $65.70   $65.70   $65.70  
  Purchase #2 $150.43   13.327%   $170.4778   $170.48   $170.50   $170.50  
  Purchase #3 $24.44   12.250%   $27.4339   $27.43   $27.45   $27.40  
  Purchase #4 $133.60   8.364%   $144.7743   $144.77   $144.75   $144.80  
  Purchase #5 $53.42   6.461%   $56.8715   $56.87   $56.85   $56.90  
  Purchase #6 $18.85   5.723%   $19.9288   $19.93   $19.95   $19.90  
  Purchase #7 $186.27   3.200%   $192.2306   $192.23   $192.25   $192.20  
  7 purchase totals = $629.29       $677.4123   $677.41   $677.45   $677.40