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 $56.59   13.520%   $64.241   $64.24   $64.25   $64.20  
  Purchase #2 $111.35   5.385%   $117.3462   $117.35   $117.35   $117.30  
  Purchase #3 $160.69   5.149%   $168.9639   $168.96   $168.95   $169.00  
  Purchase #4 $159.43   11.405%   $177.613   $177.61   $177.60   $177.60  
  Purchase #5 $214.43   10.504%   $236.9537   $236.95   $236.95   $237.00  
  Purchase #6 $88.78   6.339%   $94.4078   $94.41   $94.40   $94.40  
  Purchase #7 $113.48   13.506%   $128.8066   $128.81   $128.80   $128.80  
  7 purchase totals = $904.75       $988.3322   $988.33   $988.30   $988.30