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 $56.62   5.873%   $59.9453   $59.95   $59.95   $59.90  
  Purchase #2 $196.55   4.369%   $205.1373   $205.14   $205.15   $205.10  
  Purchase #3 $88.51   8.754%   $96.2582   $96.26   $96.25   $96.30  
  Purchase #4 $137.92   12.735%   $155.4841   $155.48   $155.50   $155.50  
  Purchase #5 $44.92   9.222%   $49.0625   $49.06   $49.05   $49.10  
  Purchase #6 $244.84   3.276%   $252.861   $252.86   $252.85   $252.90  
  Purchase #7 $123.45   8.402%   $133.8223   $133.82   $133.80   $133.80  
  7 purchase totals = $892.81       $952.5707   $952.57   $952.55   $952.60