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 $154.36   5.769%   $163.265   $163.27   $163.25   $163.30  
  Purchase #2 $51.92   5.635%   $54.8457   $54.85   $54.85   $54.80  
  Purchase #3 $176.49   3.687%   $182.9972   $183.00   $183.00   $183.00  
  Purchase #4 $217.43   4.642%   $227.5231   $227.52   $227.50   $227.50  
  Purchase #5 $211.63   5.279%   $222.8019   $222.80   $222.80   $222.80  
  Purchase #6 $240.55   5.355%   $253.4315   $253.43   $253.45   $253.40  
  Purchase #7 $169.94   10.635%   $188.0131   $188.01   $188.00   $188.00  
  7 purchase totals = $1,222.32       $1,292.8775   $1,292.88   $1,292.85   $1,292.80