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 $167.82   10.753%   $185.8657   $185.87   $185.85   $185.90  
  Purchase #2 $234.57   7.686%   $252.5991   $252.60   $252.60   $252.60  
  Purchase #3 $121.45   7.105%   $130.079   $130.08   $130.10   $130.10  
  Purchase #4 $48.92   9.486%   $53.5606   $53.56   $53.55   $53.60  
  Purchase #5 $123.59   3.197%   $127.5412   $127.54   $127.55   $127.50  
  Purchase #6 $230.42   9.362%   $251.9919   $251.99   $252.00   $252.00  
  Purchase #7 $125.94   7.213%   $135.0241   $135.02   $135.00   $135.00  
  7 purchase totals = $1,052.71       $1,136.6616   $1,136.66   $1,136.65   $1,136.70