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 $148.88   11.713%   $166.3183   $166.32   $166.30   $166.30  
  Purchase #2 $232.32   8.796%   $252.7549   $252.75   $252.75   $252.80  
  Purchase #3 $53.90   9.529%   $59.0361   $59.04   $59.05   $59.00  
  Purchase #4 $208.57   11.561%   $232.6828   $232.68   $232.70   $232.70  
  Purchase #5 $45.61   5.727%   $48.2221   $48.22   $48.20   $48.20  
  Purchase #6 $160.47   9.230%   $175.2814   $175.28   $175.30   $175.30  
  Purchase #7 $115.89   13.381%   $131.3972   $131.40   $131.40   $131.40  
  7 purchase totals = $965.64       $1,065.6928   $1,065.69   $1,065.70   $1,065.70