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 $239.84   13.518%   $272.2616   $272.26   $272.25   $272.30  
  Purchase #2 $61.83   8.411%   $67.0305   $67.03   $67.05   $67.00  
  Purchase #3 $197.34   5.741%   $208.6693   $208.67   $208.65   $208.70  
  Purchase #4 $52.44   5.620%   $55.3871   $55.39   $55.40   $55.40  
  Purchase #5 $92.43   5.700%   $97.6985   $97.70   $97.70   $97.70  
  Purchase #6 $237.61   12.669%   $267.7128   $267.71   $267.70   $267.70  
  Purchase #7 $145.96   3.613%   $151.2335   $151.23   $151.25   $151.20  
  7 purchase totals = $1,027.45       $1,119.9933   $1,119.99   $1,120.00   $1,120.00