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 $63.82   3.274%   $65.9095   $65.91   $65.90   $65.90  
  Purchase #2 $174.80   10.663%   $193.4389   $193.44   $193.45   $193.40  
  Purchase #3 $108.64   13.375%   $123.1706   $123.17   $123.15   $123.20  
  Purchase #4 $245.43   9.272%   $268.1863   $268.19   $268.20   $268.20  
  Purchase #5 $25.91   4.558%   $27.091   $27.09   $27.10   $27.10  
  Purchase #6 $126.67   12.639%   $142.6798   $142.68   $142.70   $142.70  
  Purchase #7 $218.46   13.268%   $247.4453   $247.45   $247.45   $247.40  
  7 purchase totals = $963.73       $1,067.9214   $1,067.93   $1,067.95   $1,067.90