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 $75.62   5.535%   $79.8056   $79.81   $79.80   $79.80  
  Purchase #2 $181.84   10.703%   $201.3023   $201.30   $201.30   $201.30  
  Purchase #3 $185.48   11.153%   $206.1666   $206.17   $206.15   $206.20  
  Purchase #4 $82.86   10.695%   $91.7219   $91.72   $91.70   $91.70  
  Purchase #5 $89.68   3.296%   $92.6359   $92.64   $92.65   $92.60  
  Purchase #6 $240.74   3.740%   $249.7437   $249.74   $249.75   $249.70  
  Purchase #7 $91.75   6.781%   $97.9716   $97.97   $97.95   $98.00  
  7 purchase totals = $947.97       $1,019.3476   $1,019.35   $1,019.30   $1,019.30