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 $53.57   9.508%   $58.6634   $58.66   $58.65   $58.70  
  Purchase #2 $248.58   10.227%   $274.0023   $274.00   $274.00   $274.00  
  Purchase #3 $170.35   6.177%   $180.8725   $180.87   $180.85   $180.90  
  Purchase #4 $232.59   7.626%   $250.3273   $250.33   $250.35   $250.30  
  Purchase #5 $185.71   9.113%   $202.6338   $202.63   $202.65   $202.60  
  Purchase #6 $248.69   8.224%   $269.1423   $269.14   $269.15   $269.10  
  Purchase #7 $241.27   3.348%   $249.3477   $249.35   $249.35   $249.30  
  7 purchase totals = $1,380.76       $1,484.9893   $1,484.98   $1,485.00   $1,484.90