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 $101.80   9.637%   $111.6105   $111.61   $111.60   $111.60  
  Purchase #2 $130.30   13.256%   $147.5726   $147.57   $147.55   $147.60  
  Purchase #3 $60.33   6.476%   $64.237   $64.24   $64.25   $64.20  
  Purchase #4 $50.44   9.491%   $55.2273   $55.23   $55.25   $55.20  
  Purchase #5 $216.67   4.865%   $227.211   $227.21   $227.20   $227.20  
  Purchase #6 $242.78   9.324%   $265.4168   $265.42   $265.40   $265.40  
  Purchase #7 $173.48   4.200%   $180.7662   $180.77   $180.75   $180.80  
  7 purchase totals = $975.80       $1,052.0414   $1,052.05   $1,052.00   $1,052.00