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 $202.90   11.676%   $226.5906   $226.59   $226.60   $226.60  
  Purchase #2 $199.32   3.703%   $206.7008   $206.70   $206.70   $206.70  
  Purchase #3 $168.93   8.520%   $183.3228   $183.32   $183.30   $183.30  
  Purchase #4 $230.37   8.744%   $250.5136   $250.51   $250.50   $250.50  
  Purchase #5 $59.65   12.304%   $66.9893   $66.99   $67.00   $67.00  
  Purchase #6 $26.58   5.452%   $28.0291   $28.03   $28.05   $28.00  
  Purchase #7 $49.74   3.645%   $51.553   $51.55   $51.55   $51.60  
  7 purchase totals = $937.49       $1,013.6992   $1,013.69   $1,013.70   $1,013.70