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 $33.87   5.790%   $35.8311   $35.83   $35.85   $35.80  
  Purchase #2 $82.85   4.232%   $86.3562   $86.36   $86.35   $86.40  
  Purchase #3 $110.60   3.291%   $114.2398   $114.24   $114.25   $114.20  
  Purchase #4 $132.26   3.738%   $137.2039   $137.20   $137.20   $137.20  
  Purchase #5 $221.48   3.335%   $228.8664   $228.87   $228.85   $228.90  
  Purchase #6 $123.44   5.478%   $130.202   $130.20   $130.20   $130.20  
  Purchase #7 $216.72   12.598%   $244.0224   $244.02   $244.00   $244.00  
  7 purchase totals = $921.22       $976.7218   $976.72   $976.70   $976.70