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 $207.63   11.627%   $231.7711   $231.77   $231.75   $231.80  
  Purchase #2 $156.62   10.257%   $172.6845   $172.68   $172.70   $172.70  
  Purchase #3 $184.93   10.286%   $203.9519   $203.95   $203.95   $204.00  
  Purchase #4 $63.39   10.767%   $70.2152   $70.22   $70.20   $70.20  
  Purchase #5 $87.69   3.168%   $90.468   $90.47   $90.45   $90.50  
  Purchase #6 $238.41   8.844%   $259.495   $259.50   $259.50   $259.50  
  Purchase #7 $146.48   9.380%   $160.2198   $160.22   $160.20   $160.20  
  7 purchase totals = $1,085.15       $1,188.8055   $1,188.81   $1,188.75   $1,188.90