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 $43.64   7.469%   $46.8995   $46.90   $46.90   $46.90  
  Purchase #2 $235.88   10.862%   $261.5013   $261.50   $261.50   $261.50  
  Purchase #3 $130.73   6.698%   $139.4863   $139.49   $139.50   $139.50  
  Purchase #4 $180.53   4.751%   $189.107   $189.11   $189.10   $189.10  
  Purchase #5 $53.50   8.396%   $57.9919   $57.99   $58.00   $58.00  
  Purchase #6 $98.95   12.263%   $111.0842   $111.08   $111.10   $111.10  
  Purchase #7 $144.41   13.556%   $163.9862   $163.99   $164.00   $164.00  
  7 purchase totals = $887.64       $970.0564   $970.06   $970.10   $970.10