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 $103.26   13.244%   $116.9358   $116.94   $116.95   $116.90  
  Purchase #2 $118.69   13.308%   $134.4853   $134.49   $134.50   $134.50  
  Purchase #3 $226.57   10.196%   $249.6711   $249.67   $249.65   $249.70  
  Purchase #4 $32.56   4.395%   $33.991   $33.99   $34.00   $34.00  
  Purchase #5 $215.84   9.231%   $235.7642   $235.76   $235.75   $235.80  
  Purchase #6 $50.34   6.391%   $53.5572   $53.56   $53.55   $53.60  
  Purchase #7 $232.36   7.627%   $250.0821   $250.08   $250.10   $250.10  
  7 purchase totals = $979.62       $1,074.4867   $1,074.49   $1,074.50   $1,074.60