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 $67.88   9.615%   $74.4067   $74.41   $74.40   $74.40  
  Purchase #2 $129.68   4.129%   $135.0345   $135.03   $135.05   $135.00  
  Purchase #3 $187.30   10.461%   $206.8935   $206.89   $206.90   $206.90  
  Purchase #4 $162.54   6.613%   $173.2888   $173.29   $173.30   $173.30  
  Purchase #5 $152.75   6.627%   $162.8727   $162.87   $162.85   $162.90  
  Purchase #6 $6.57   4.252%   $6.8494   $6.85   $6.85   $6.80  
  Purchase #7 $234.86   13.273%   $266.033   $266.03   $266.05   $266.00  
  7 purchase totals = $941.58       $1,025.3786   $1,025.37   $1,025.40   $1,025.30