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 $68.67   4.192%   $71.5486   $71.55   $71.55   $71.50  
  Purchase #2 $11.28   3.342%   $11.657   $11.66   $11.65   $11.70  
  Purchase #3 $18.26   4.848%   $19.1452   $19.15   $19.15   $19.10  
  Purchase #4 $52.97   11.849%   $59.2464   $59.25   $59.25   $59.20  
  Purchase #5 $169.62   6.872%   $181.2763   $181.28   $181.30   $181.30  
  Purchase #6 $61.26   3.525%   $63.4194   $63.42   $63.40   $63.40  
  Purchase #7 $113.30   5.558%   $119.5972   $119.60   $119.60   $119.60  
  7 purchase totals = $495.36       $525.8901   $525.91   $525.90   $525.80