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 $124.99   8.545%   $135.6704   $135.67   $135.65   $135.70  
  Purchase #2 $25.70   13.516%   $29.1736   $29.17   $29.15   $29.20  
  Purchase #3 $172.29   7.718%   $185.5873   $185.59   $185.60   $185.60  
  Purchase #4 $36.26   12.831%   $40.9125   $40.91   $40.90   $40.90  
  Purchase #5 $234.56   8.130%   $253.6297   $253.63   $253.65   $253.60  
  Purchase #6 $250.74   8.614%   $272.3387   $272.34   $272.35   $272.30  
  Purchase #7 $107.65   8.210%   $116.4881   $116.49   $116.50   $116.50  
  7 purchase totals = $952.19       $1,033.8003   $1,033.80   $1,033.80   $1,033.80