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 $81.27   8.334%   $88.043   $88.04   $88.05   $88.00  
  Purchase #2 $125.90   7.650%   $135.5314   $135.53   $135.55   $135.50  
  Purchase #3 $25.98   4.462%   $27.1392   $27.14   $27.15   $27.10  
  Purchase #4 $165.85   3.262%   $171.26   $171.26   $171.25   $171.30  
  Purchase #5 $226.45   9.508%   $247.9809   $247.98   $248.00   $248.00  
  Purchase #6 $47.95   11.552%   $53.4892   $53.49   $53.50   $53.50  
  Purchase #7 $190.70   13.443%   $216.3358   $216.34   $216.35   $216.30  
  7 purchase totals = $864.10       $939.7795   $939.78   $939.85   $939.70