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 $211.39   9.557%   $231.5925   $231.59   $231.60   $231.60  
  Purchase #2 $158.98   4.565%   $166.2374   $166.24   $166.25   $166.20  
  Purchase #3 $151.74   6.293%   $161.289   $161.29   $161.30   $161.30  
  Purchase #4 $219.62   10.515%   $242.713   $242.71   $242.70   $242.70  
  Purchase #5 $63.75   9.846%   $70.0268   $70.03   $70.05   $70.00  
  Purchase #6 $204.51   5.838%   $216.4493   $216.45   $216.45   $216.40  
  Purchase #7 $93.45   8.493%   $101.3867   $101.39   $101.40   $101.40  
  7 purchase totals = $1,103.44       $1,189.6947   $1,189.70   $1,189.75   $1,189.60