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 $67.96   13.254%   $76.9674   $76.97   $76.95   $77.00  
  Purchase #2 $56.99   13.689%   $64.7914   $64.79   $64.80   $64.80  
  Purchase #3 $233.99   5.120%   $245.9703   $245.97   $245.95   $246.00  
  Purchase #4 $30.95   8.240%   $33.5003   $33.50   $33.50   $33.50  
  Purchase #5 $193.82   11.413%   $215.9407   $215.94   $215.95   $215.90  
  Purchase #6 $102.82   5.562%   $108.5388   $108.54   $108.55   $108.50  
  Purchase #7 $247.83   8.746%   $269.5052   $269.51   $269.50   $269.50  
  7 purchase totals = $934.36       $1,015.2141   $1,015.22   $1,015.20   $1,015.20