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 $199.58   10.771%   $221.0768   $221.08   $221.10   $221.10  
  Purchase #2 $47.92   3.532%   $49.6125   $49.61   $49.60   $49.60  
  Purchase #3 $171.84   7.433%   $184.6129   $184.61   $184.60   $184.60  
  Purchase #4 $76.71   10.283%   $84.5981   $84.60   $84.60   $84.60  
  Purchase #5 $161.26   3.638%   $167.1266   $167.13   $167.15   $167.10  
  Purchase #6 $213.55   12.671%   $240.6089   $240.61   $240.60   $240.60  
  Purchase #7 $53.75   13.277%   $60.8864   $60.89   $60.90   $60.90  
  7 purchase totals = $924.61       $1,008.5222   $1,008.53   $1,008.55   $1,008.50