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 $24.86   5.786%   $26.2984   $26.30   $26.30   $26.30  
  Purchase #2 $92.30   7.688%   $99.396   $99.40   $99.40   $99.40  
  Purchase #3 $87.64   3.840%   $91.0054   $91.01   $91.00   $91.00  
  Purchase #4 $250.31   4.194%   $260.808   $260.81   $260.80   $260.80  
  Purchase #5 $50.62   11.640%   $56.5122   $56.51   $56.50   $56.50  
  Purchase #6 $63.50   5.299%   $66.8649   $66.86   $66.85   $66.90  
  Purchase #7 $240.45   6.166%   $255.2761   $255.28   $255.30   $255.30  
  7 purchase totals = $809.68       $856.1610   $856.17   $856.15   $856.20