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 $144.86   5.661%   $153.0605   $153.06   $153.05   $153.10  
  Purchase #2 $153.35   13.245%   $173.6612   $173.66   $173.65   $173.70  
  Purchase #3 $237.95   11.226%   $264.6623   $264.66   $264.65   $264.70  
  Purchase #4 $19.51   6.216%   $20.7227   $20.72   $20.70   $20.70  
  Purchase #5 $79.77   5.613%   $84.2475   $84.25   $84.25   $84.20  
  Purchase #6 $46.30   6.833%   $49.4637   $49.46   $49.45   $49.50  
  Purchase #7 $207.70   3.259%   $214.4689   $214.47   $214.45   $214.50  
  7 purchase totals = $889.44       $960.2868   $960.28   $960.20   $960.40