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 $248.33   10.594%   $274.6381   $274.64   $274.65   $274.60  
  Purchase #2 $231.81   9.802%   $254.532   $254.53   $254.55   $254.50  
  Purchase #3 $176.44   11.761%   $197.1911   $197.19   $197.20   $197.20  
  Purchase #4 $57.46   5.748%   $60.7628   $60.76   $60.75   $60.80  
  Purchase #5 $152.52   13.690%   $173.4   $173.40   $173.40   $173.40  
  Purchase #6 $161.81   11.598%   $180.5767   $180.58   $180.60   $180.60  
  Purchase #7 $153.96   11.833%   $172.1781   $172.18   $172.20   $172.20  
  7 purchase totals = $1,182.33       $1,313.2788   $1,313.28   $1,313.35   $1,313.30