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 $162.96   10.831%   $180.6102   $180.61   $180.60   $180.60  
  Purchase #2 $219.69   11.367%   $244.6622   $244.66   $244.65   $244.70  
  Purchase #3 $74.37   13.228%   $84.2077   $84.21   $84.20   $84.20  
  Purchase #4 $169.64   11.662%   $189.4234   $189.42   $189.40   $189.40  
  Purchase #5 $228.57   9.813%   $250.9996   $251.00   $251.00   $251.00  
  Purchase #6 $96.54   11.675%   $107.811   $107.81   $107.80   $107.80  
  Purchase #7 $219.67   8.460%   $238.2541   $238.25   $238.25   $238.30  
  7 purchase totals = $1,171.44       $1,295.9682   $1,295.96   $1,295.90   $1,296.00