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 $68.86   11.867%   $77.0316   $77.03   $77.05   $77.00  
  Purchase #2 $93.55   12.312%   $105.0679   $105.07   $105.05   $105.10  
  Purchase #3 $250.94   4.601%   $262.4857   $262.49   $262.50   $262.50  
  Purchase #4 $225.81   10.331%   $249.1384   $249.14   $249.15   $249.10  
  Purchase #5 $224.92   9.544%   $246.3864   $246.39   $246.40   $246.40  
  Purchase #6 $46.54   12.122%   $52.1816   $52.18   $52.20   $52.20  
  Purchase #7 $224.53   7.740%   $241.9086   $241.91   $241.90   $241.90  
  7 purchase totals = $1,135.15       $1,234.2002   $1,234.21   $1,234.25   $1,234.20