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 $198.99   13.719%   $226.2894   $226.29   $226.30   $226.30  
  Purchase #2 $54.62   11.124%   $60.6959   $60.70   $60.70   $60.70  
  Purchase #3 $158.61   3.295%   $163.8362   $163.84   $163.85   $163.80  
  Purchase #4 $70.25   8.857%   $76.472   $76.47   $76.45   $76.50  
  Purchase #5 $158.86   7.837%   $171.3099   $171.31   $171.30   $171.30  
  Purchase #6 $165.47   8.220%   $179.0716   $179.07   $179.05   $179.10  
  Purchase #7 $139.59   13.315%   $158.1764   $158.18   $158.20   $158.20  
  7 purchase totals = $946.39       $1,035.8514   $1,035.86   $1,035.85   $1,035.90