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 $136.53   13.540%   $155.0162   $155.02   $155.00   $155.00  
  Purchase #2 $73.28   13.777%   $83.3758   $83.38   $83.40   $83.40  
  Purchase #3 $187.40   12.542%   $210.9037   $210.90   $210.90   $210.90  
  Purchase #4 $179.55   11.822%   $200.7764   $200.78   $200.80   $200.80  
  Purchase #5 $12.28   10.873%   $13.6152   $13.62   $13.60   $13.60  
  Purchase #6 $247.69   10.724%   $274.2523   $274.25   $274.25   $274.30  
  Purchase #7 $64.94   12.816%   $73.2627   $73.26   $73.25   $73.30  
  7 purchase totals = $901.67       $1,011.2023   $1,011.21   $1,011.20   $1,011.30