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 $50.49   11.425%   $56.2585   $56.26   $56.25   $56.30  
  Purchase #2 $200.58   9.317%   $219.268   $219.27   $219.25   $219.30  
  Purchase #3 $124.75   11.727%   $139.3794   $139.38   $139.40   $139.40  
  Purchase #4 $205.42   3.229%   $212.053   $212.05   $212.05   $212.10  
  Purchase #5 $144.53   13.819%   $164.5026   $164.50   $164.50   $164.50  
  Purchase #6 $62.40   13.539%   $70.8483   $70.85   $70.85   $70.80  
  Purchase #7 $189.74   13.414%   $215.1917   $215.19   $215.20   $215.20  
  7 purchase totals = $977.91       $1,077.5015   $1,077.50   $1,077.50   $1,077.60