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 $108.28   6.166%   $114.9565   $114.96   $114.95   $115.00  
  Purchase #2 $232.83   11.366%   $259.2935   $259.29   $259.30   $259.30  
  Purchase #3 $248.25   9.638%   $272.1763   $272.18   $272.20   $272.20  
  Purchase #4 $120.74   9.290%   $131.9567   $131.96   $131.95   $132.00  
  Purchase #5 $106.70   13.685%   $121.3019   $121.30   $121.30   $121.30  
  Purchase #6 $65.34   3.485%   $67.6171   $67.62   $67.60   $67.60  
  Purchase #7 $177.58   12.142%   $199.1418   $199.14   $199.15   $199.10  
  7 purchase totals = $1,059.72       $1,166.4438   $1,166.45   $1,166.45   $1,166.50