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 $70.42   13.156%   $79.6845   $79.68   $79.70   $79.70  
  Purchase #2 $138.55   5.322%   $145.9236   $145.92   $145.90   $145.90  
  Purchase #3 $171.72   4.287%   $179.0816   $179.08   $179.10   $179.10  
  Purchase #4 $43.51   11.693%   $48.5976   $48.60   $48.60   $48.60  
  Purchase #5 $127.45   7.314%   $136.7717   $136.77   $136.75   $136.80  
  Purchase #6 $63.74   4.686%   $66.7269   $66.73   $66.75   $66.70  
  Purchase #7 $200.40   13.463%   $227.3799   $227.38   $227.40   $227.40  
  7 purchase totals = $815.79       $884.1658   $884.16   $884.20   $884.20