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 $81.82   13.801%   $93.112   $93.11   $93.10   $93.10  
  Purchase #2 $129.26   9.213%   $141.1687   $141.17   $141.15   $141.20  
  Purchase #3 $214.34   9.357%   $234.3958   $234.40   $234.40   $234.40  
  Purchase #4 $163.78   3.466%   $169.4566   $169.46   $169.45   $169.50  
  Purchase #5 $244.32   4.305%   $254.838   $254.84   $254.85   $254.80  
  Purchase #6 $84.46   4.468%   $88.2337   $88.23   $88.25   $88.20  
  Purchase #7 $153.87   8.127%   $166.375   $166.38   $166.40   $166.40  
  7 purchase totals = $1,071.85       $1,147.5798   $1,147.59   $1,147.60   $1,147.60