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 $78.92   5.109%   $82.952   $82.95   $82.95   $83.00  
  Purchase #2 $184.93   12.476%   $208.0019   $208.00   $208.00   $208.00  
  Purchase #3 $250.26   6.403%   $266.2841   $266.28   $266.30   $266.30  
  Purchase #4 $208.42   11.419%   $232.2195   $232.22   $232.20   $232.20  
  Purchase #5 $113.30   11.622%   $126.4677   $126.47   $126.45   $126.50  
  Purchase #6 $232.30   9.452%   $254.257   $254.26   $254.25   $254.30  
  Purchase #7 $120.33   6.718%   $128.4138   $128.41   $128.40   $128.40  
  7 purchase totals = $1,188.46       $1,298.5960   $1,298.59   $1,298.55   $1,298.70