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 $191.92   11.260%   $213.5302   $213.53   $213.55   $213.50  
  Purchase #2 $57.77   5.696%   $61.0606   $61.06   $61.05   $61.10  
  Purchase #3 $178.45   6.190%   $189.4961   $189.50   $189.50   $189.50  
  Purchase #4 $143.34   10.619%   $158.5613   $158.56   $158.55   $158.60  
  Purchase #5 $185.75   8.214%   $201.0075   $201.01   $201.00   $201.00  
  Purchase #6 $108.25   11.696%   $120.9109   $120.91   $120.90   $120.90  
  Purchase #7 $117.28   11.529%   $130.8012   $130.80   $130.80   $130.80  
  7 purchase totals = $982.76       $1,075.3678   $1,075.37   $1,075.35   $1,075.40