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 $187.29   11.482%   $208.7946   $208.79   $208.80   $208.80  
  Purchase #2 $177.93   13.810%   $202.5021   $202.50   $202.50   $202.50  
  Purchase #3 $89.61   11.280%   $99.718   $99.72   $99.70   $99.70  
  Purchase #4 $234.85   4.158%   $244.6151   $244.62   $244.60   $244.60  
  Purchase #5 $196.75   8.252%   $212.9858   $212.99   $213.00   $213.00  
  Purchase #6 $168.86   5.695%   $178.4766   $178.48   $178.50   $178.50  
  Purchase #7 $49.40   10.299%   $54.4877   $54.49   $54.50   $54.50  
  7 purchase totals = $1,104.69       $1,201.5799   $1,201.59   $1,201.60   $1,201.60