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 $136.29   11.199%   $151.5531   $151.55   $151.55   $151.60  
  Purchase #2 $202.78   7.216%   $217.4126   $217.41   $217.40   $217.40  
  Purchase #3 $243.25   13.588%   $276.3028   $276.30   $276.30   $276.30  
  Purchase #4 $177.33   8.796%   $192.9279   $192.93   $192.95   $192.90  
  Purchase #5 $85.53   13.764%   $97.3023   $97.30   $97.30   $97.30  
  Purchase #6 $220.41   8.779%   $239.7598   $239.76   $239.75   $239.80  
  Purchase #7 $60.35   10.699%   $66.8068   $66.81   $66.80   $66.80  
  7 purchase totals = $1,125.94       $1,242.0653   $1,242.06   $1,242.05   $1,242.10