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 $154.29   10.860%   $171.0459   $171.05   $171.05   $171.00  
  Purchase #2 $58.76   13.234%   $66.5363   $66.54   $66.55   $66.50  
  Purchase #3 $150.64   4.840%   $157.931   $157.93   $157.95   $157.90  
  Purchase #4 $197.90   4.222%   $206.2553   $206.26   $206.25   $206.30  
  Purchase #5 $166.93   4.398%   $174.2716   $174.27   $174.25   $174.30  
  Purchase #6 $57.64   4.196%   $60.0586   $60.06   $60.05   $60.10  
  Purchase #7 $161.37   13.284%   $182.8064   $182.81   $182.80   $182.80  
  7 purchase totals = $947.53       $1,018.9051   $1,018.92   $1,018.90   $1,018.90