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 $7.46   11.717%   $8.3341   $8.33   $8.35   $8.30  
  Purchase #2 $212.78   12.516%   $239.4115   $239.41   $239.40   $239.40  
  Purchase #3 $245.76   6.615%   $262.017   $262.02   $262.00   $262.00  
  Purchase #4 $208.45   12.348%   $234.1894   $234.19   $234.20   $234.20  
  Purchase #5 $121.74   4.296%   $126.97   $126.97   $126.95   $127.00  
  Purchase #6 $196.49   11.193%   $218.4831   $218.48   $218.50   $218.50  
  Purchase #7 $25.84   5.525%   $27.2677   $27.27   $27.25   $27.30  
  7 purchase totals = $1,018.52       $1,116.6728   $1,116.67   $1,116.65   $1,116.70