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 $81.85   4.687%   $85.6863   $85.69   $85.70   $85.70  
  Purchase #2 $157.84   11.531%   $176.0405   $176.04   $176.05   $176.00  
  Purchase #3 $126.48   12.759%   $142.6176   $142.62   $142.60   $142.60  
  Purchase #4 $10.42   6.410%   $11.0879   $11.09   $11.10   $11.10  
  Purchase #5 $197.75   6.206%   $210.0224   $210.02   $210.00   $210.00  
  Purchase #6 $245.45   8.681%   $266.7575   $266.76   $266.75   $266.80  
  Purchase #7 $129.38   3.828%   $134.3327   $134.33   $134.35   $134.30  
  7 purchase totals = $949.17       $1,026.5449   $1,026.55   $1,026.55   $1,026.50