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 $177.85   6.431%   $189.2875   $189.29   $189.30   $189.30  
  Purchase #2 $40.59   4.283%   $42.3285   $42.33   $42.35   $42.30  
  Purchase #3 $228.95   9.789%   $251.3619   $251.36   $251.35   $251.40  
  Purchase #4 $162.81   7.307%   $174.7065   $174.71   $174.70   $174.70  
  Purchase #5 $45.44   10.116%   $50.0367   $50.04   $50.05   $50.00  
  Purchase #6 $150.77   11.338%   $167.8643   $167.86   $167.85   $167.90  
  Purchase #7 $179.39   11.713%   $200.402   $200.40   $200.40   $200.40  
  7 purchase totals = $985.80       $1,075.9874   $1,075.99   $1,076.00   $1,076.00