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 $105.92   9.560%   $116.046   $116.05   $116.05   $116.00  
  Purchase #2 $224.75   9.297%   $245.645   $245.65   $245.65   $245.60  
  Purchase #3 $53.53   12.658%   $60.3058   $60.31   $60.30   $60.30  
  Purchase #4 $153.26   10.550%   $169.4289   $169.43   $169.45   $169.40  
  Purchase #5 $214.84   11.693%   $239.9612   $239.96   $239.95   $240.00  
  Purchase #6 $248.85   3.262%   $256.9675   $256.97   $256.95   $257.00  
  Purchase #7 $74.30   12.508%   $83.5934   $83.59   $83.60   $83.60  
  7 purchase totals = $1,075.45       $1,171.9478   $1,171.96   $1,171.95   $1,171.90