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 $67.72   13.846%   $77.0965   $77.10   $77.10   $77.10  
  Purchase #2 $248.44   8.600%   $269.8058   $269.81   $269.80   $269.80  
  Purchase #3 $65.58   4.614%   $68.6059   $68.61   $68.60   $68.60  
  Purchase #4 $102.71   4.439%   $107.2693   $107.27   $107.25   $107.30  
  Purchase #5 $165.26   12.774%   $186.3703   $186.37   $186.35   $186.40  
  Purchase #6 $145.58   9.162%   $158.918   $158.92   $158.90   $158.90  
  Purchase #7 $172.37   11.604%   $192.3718   $192.37   $192.35   $192.40  
  7 purchase totals = $967.66       $1,060.4376   $1,060.45   $1,060.35   $1,060.50