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 $62.84   10.202%   $69.2509   $69.25   $69.25   $69.30  
  Purchase #2 $49.95   9.233%   $54.5619   $54.56   $54.55   $54.60  
  Purchase #3 $102.44   7.800%   $110.4303   $110.43   $110.45   $110.40  
  Purchase #4 $246.58   10.619%   $272.7643   $272.76   $272.75   $272.80  
  Purchase #5 $24.84   7.440%   $26.6881   $26.69   $26.70   $26.70  
  Purchase #6 $245.51   5.670%   $259.4304   $259.43   $259.45   $259.40  
  Purchase #7 $33.41   7.820%   $36.0227   $36.02   $36.00   $36.00  
  7 purchase totals = $765.57       $829.1486   $829.14   $829.15   $829.20