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 $163.69   12.517%   $184.1791   $184.18   $184.20   $184.20  
  Purchase #2 $32.34   10.237%   $35.6506   $35.65   $35.65   $35.70  
  Purchase #3 $221.46   13.315%   $250.9474   $250.95   $250.95   $250.90  
  Purchase #4 $235.84   3.775%   $244.743   $244.74   $244.75   $244.70  
  Purchase #5 $167.93   6.789%   $179.3308   $179.33   $179.35   $179.30  
  Purchase #6 $85.67   3.523%   $88.6882   $88.69   $88.70   $88.70  
  Purchase #7 $177.82   8.263%   $192.5133   $192.51   $192.50   $192.50  
  7 purchase totals = $1,084.75       $1,176.0524   $1,176.05   $1,176.10   $1,176.00