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 $157.91   13.513%   $179.2484   $179.25   $179.25   $179.20  
  Purchase #2 $134.49   9.782%   $147.6458   $147.65   $147.65   $147.60  
  Purchase #3 $153.44   10.375%   $169.3594   $169.36   $169.35   $169.40  
  Purchase #4 $229.88   5.237%   $241.9188   $241.92   $241.90   $241.90  
  Purchase #5 $48.80   4.348%   $50.9218   $50.92   $50.90   $50.90  
  Purchase #6 $152.47   9.256%   $166.5826   $166.58   $166.60   $166.60  
  Purchase #7 $184.93   11.483%   $206.1655   $206.17   $206.15   $206.20  
  7 purchase totals = $1,061.92       $1,161.8423   $1,161.85   $1,161.80   $1,161.80