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 $59.58   12.512%   $67.0346   $67.03   $67.05   $67.00  
  Purchase #2 $122.51   12.317%   $137.5996   $137.60   $137.60   $137.60  
  Purchase #3 $48.93   9.158%   $53.411   $53.41   $53.40   $53.40  
  Purchase #4 $63.69   8.781%   $69.2826   $69.28   $69.30   $69.30  
  Purchase #5 $241.51   10.659%   $267.2526   $267.25   $267.25   $267.30  
  Purchase #6 $202.43   9.605%   $221.8734   $221.87   $221.85   $221.90  
  Purchase #7 $171.98   10.337%   $189.7576   $189.76   $189.75   $189.80  
  7 purchase totals = $910.63       $1,006.2114   $1,006.20   $1,006.20   $1,006.30