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 $87.27   10.547%   $96.4744   $96.47   $96.45   $96.50  
  Purchase #2 $188.53   10.332%   $208.0089   $208.01   $208.00   $208.00  
  Purchase #3 $248.58   4.713%   $260.2956   $260.30   $260.30   $260.30  
  Purchase #4 $59.56   6.612%   $63.4981   $63.50   $63.50   $63.50  
  Purchase #5 $67.58   10.107%   $74.4103   $74.41   $74.40   $74.40  
  Purchase #6 $129.55   7.734%   $139.5694   $139.57   $139.55   $139.60  
  Purchase #7 $196.42   13.588%   $223.1095   $223.11   $223.10   $223.10  
  7 purchase totals = $977.49       $1,065.3662   $1,065.37   $1,065.30   $1,065.40