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 $246.71   7.798%   $265.9484   $265.95   $265.95   $265.90  
  Purchase #2 $47.27   12.176%   $53.0256   $53.03   $53.05   $53.00  
  Purchase #3 $75.75   11.336%   $84.337   $84.34   $84.35   $84.30  
  Purchase #4 $147.49   11.327%   $164.1962   $164.20   $164.20   $164.20  
  Purchase #5 $177.56   5.476%   $187.2832   $187.28   $187.30   $187.30  
  Purchase #6 $184.92   10.570%   $204.466   $204.47   $204.45   $204.50  
  Purchase #7 $43.92   8.215%   $47.528   $47.53   $47.55   $47.50  
  7 purchase totals = $923.62       $1,006.7844   $1,006.80   $1,006.85   $1,006.70