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 $100.58   9.180%   $109.8132   $109.81   $109.80   $109.80  
  Purchase #2 $40.80   8.448%   $44.2468   $44.25   $44.25   $44.20  
  Purchase #3 $157.27   10.669%   $174.0491   $174.05   $174.05   $174.00  
  Purchase #4 $80.70   8.327%   $87.4199   $87.42   $87.40   $87.40  
  Purchase #5 $142.51   3.469%   $147.4537   $147.45   $147.45   $147.50  
  Purchase #6 $176.88   10.292%   $195.0845   $195.08   $195.10   $195.10  
  Purchase #7 $72.36   8.638%   $78.6105   $78.61   $78.60   $78.60  
  7 purchase totals = $771.10       $836.6777   $836.67   $836.65   $836.60