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 $47.68   11.217%   $53.0283   $53.03   $53.05   $53.00  
  Purchase #2 $130.54   10.332%   $144.0274   $144.03   $144.05   $144.00  
  Purchase #3 $176.42   4.256%   $183.9284   $183.93   $183.95   $183.90  
  Purchase #4 $171.79   9.858%   $188.7251   $188.73   $188.75   $188.70  
  Purchase #5 $123.69   4.539%   $129.3043   $129.30   $129.30   $129.30  
  Purchase #6 $243.58   9.653%   $267.0928   $267.09   $267.10   $267.10  
  Purchase #7 $108.57   4.615%   $113.5805   $113.58   $113.60   $113.60  
  7 purchase totals = $1,002.27       $1,079.6868   $1,079.69   $1,079.80   $1,079.60