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 $234.46   10.659%   $259.4511   $259.45   $259.45   $259.50  
  Purchase #2 $162.63   6.786%   $173.6661   $173.67   $173.65   $173.70  
  Purchase #3 $188.31   9.860%   $206.8774   $206.88   $206.90   $206.90  
  Purchase #4 $20.52   9.692%   $22.5088   $22.51   $22.50   $22.50  
  Purchase #5 $154.76   11.662%   $172.8081   $172.81   $172.80   $172.80  
  Purchase #6 $106.93   10.184%   $117.8198   $117.82   $117.80   $117.80  
  Purchase #7 $92.78   6.146%   $98.4823   $98.48   $98.50   $98.50  
  7 purchase totals = $960.39       $1,051.6136   $1,051.62   $1,051.60   $1,051.70