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 $41.68   5.689%   $44.0512   $44.05   $44.05   $44.10  
  Purchase #2 $54.67   12.405%   $61.4518   $61.45   $61.45   $61.50  
  Purchase #3 $14.25   13.201%   $16.1311   $16.13   $16.15   $16.10  
  Purchase #4 $139.30   7.457%   $149.6876   $149.69   $149.70   $149.70  
  Purchase #5 $133.25   5.769%   $140.9372   $140.94   $140.95   $140.90  
  Purchase #6 $50.72   11.176%   $56.3885   $56.39   $56.40   $56.40  
  Purchase #7 $219.60   7.264%   $235.5517   $235.55   $235.55   $235.60  
  7 purchase totals = $653.47       $704.1991   $704.20   $704.25   $704.30