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 $60.28   9.513%   $66.0144   $66.01   $66.00   $66.00  
  Purchase #2 $229.62   10.607%   $253.9758   $253.98   $254.00   $254.00  
  Purchase #3 $48.86   9.662%   $53.5809   $53.58   $53.60   $53.60  
  Purchase #4 $245.81   12.464%   $276.4478   $276.45   $276.45   $276.40  
  Purchase #5 $139.83   12.608%   $157.4598   $157.46   $157.45   $157.50  
  Purchase #6 $64.59   6.146%   $68.5597   $68.56   $68.55   $68.60  
  Purchase #7 $122.28   6.119%   $129.7623   $129.76   $129.75   $129.80  
  7 purchase totals = $911.27       $1,005.8007   $1,005.80   $1,005.80   $1,005.90