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 $53.35   12.771%   $60.1633   $60.16   $60.15   $60.20  
  Purchase #2 $169.96   9.531%   $186.1589   $186.16   $186.15   $186.20  
  Purchase #3 $57.61   10.371%   $63.5847   $63.58   $63.60   $63.60  
  Purchase #4 $35.50   3.424%   $36.7155   $36.72   $36.70   $36.70  
  Purchase #5 $243.34   10.833%   $269.701   $269.70   $269.70   $269.70  
  Purchase #6 $97.85   11.794%   $109.3904   $109.39   $109.40   $109.40  
  Purchase #7 $243.46   6.632%   $259.6063   $259.61   $259.60   $259.60  
  7 purchase totals = $901.07       $985.3201   $985.32   $985.30   $985.40