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 $211.58   13.235%   $239.5826   $239.58   $239.60   $239.60  
  Purchase #2 $226.49   10.664%   $250.6429   $250.64   $250.65   $250.60  
  Purchase #3 $162.61   10.874%   $180.2922   $180.29   $180.30   $180.30  
  Purchase #4 $129.59   11.323%   $144.2635   $144.26   $144.25   $144.30  
  Purchase #5 $8.46   6.843%   $9.0389   $9.04   $9.05   $9.00  
  Purchase #6 $173.66   8.116%   $187.7542   $187.75   $187.75   $187.80  
  Purchase #7 $229.61   5.834%   $243.0054   $243.01   $243.00   $243.00  
  7 purchase totals = $1,142.00       $1,254.5797   $1,254.57   $1,254.60   $1,254.60