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 $59.29   8.519%   $64.3409   $64.34   $64.35   $64.30  
  Purchase #2 $227.88   12.527%   $256.4265   $256.43   $256.45   $256.40  
  Purchase #3 $228.86   10.773%   $253.5151   $253.52   $253.50   $253.50  
  Purchase #4 $234.65   5.700%   $248.0251   $248.03   $248.05   $248.00  
  Purchase #5 $89.73   6.517%   $95.5777   $95.58   $95.60   $95.60  
  Purchase #6 $189.27   13.263%   $214.3729   $214.37   $214.35   $214.40  
  Purchase #7 $166.74   6.404%   $177.418   $177.42   $177.40   $177.40  
  7 purchase totals = $1,196.42       $1,309.6762   $1,309.69   $1,309.70   $1,309.60