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 $219.49   7.678%   $236.3424   $236.34   $236.35   $236.30  
  Purchase #2 $178.31   6.846%   $190.5171   $190.52   $190.50   $190.50  
  Purchase #3 $113.35   4.610%   $118.5754   $118.58   $118.60   $118.60  
  Purchase #4 $47.74   11.859%   $53.4015   $53.40   $53.40   $53.40  
  Purchase #5 $239.56   4.224%   $249.679   $249.68   $249.70   $249.70  
  Purchase #6 $123.88   11.615%   $138.2687   $138.27   $138.25   $138.30  
  Purchase #7 $76.72   12.198%   $86.0783   $86.08   $86.10   $86.10  
  7 purchase totals = $999.05       $1,072.8624   $1,072.87   $1,072.90   $1,072.90