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 $247.52   13.552%   $281.0639   $281.06   $281.05   $281.10  
  Purchase #2 $81.90   4.462%   $85.5544   $85.55   $85.55   $85.60  
  Purchase #3 $41.63   12.682%   $46.9095   $46.91   $46.90   $46.90  
  Purchase #4 $161.55   12.817%   $182.2559   $182.26   $182.25   $182.30  
  Purchase #5 $107.28   7.257%   $115.0653   $115.07   $115.05   $115.10  
  Purchase #6 $152.73   10.269%   $168.4138   $168.41   $168.40   $168.40  
  Purchase #7 $140.43   4.869%   $147.2675   $147.27   $147.25   $147.30  
  7 purchase totals = $933.04       $1,026.5303   $1,026.53   $1,026.45   $1,026.70