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 $161.70   13.608%   $183.7041   $183.70   $183.70   $183.70  
  Purchase #2 $38.53   7.261%   $41.3277   $41.33   $41.35   $41.30  
  Purchase #3 $194.99   11.358%   $217.137   $217.14   $217.15   $217.10  
  Purchase #4 $40.92   10.744%   $45.3164   $45.32   $45.30   $45.30  
  Purchase #5 $90.42   13.443%   $102.5752   $102.58   $102.60   $102.60  
  Purchase #6 $225.56   4.592%   $235.9177   $235.92   $235.90   $235.90  
  Purchase #7 $172.60   7.247%   $185.1083   $185.11   $185.10   $185.10  
  7 purchase totals = $924.72       $1,011.0864   $1,011.10   $1,011.10   $1,011.00