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 $158.45   11.361%   $176.4515   $176.45   $176.45   $176.50  
  Purchase #2 $119.78   8.227%   $129.6343   $129.63   $129.65   $129.60  
  Purchase #3 $142.38   11.364%   $158.5601   $158.56   $158.55   $158.60  
  Purchase #4 $127.89   12.692%   $144.1218   $144.12   $144.10   $144.10  
  Purchase #5 $14.33   3.660%   $14.8545   $14.85   $14.85   $14.90  
  Purchase #6 $172.68   11.688%   $192.8628   $192.86   $192.85   $192.90  
  Purchase #7 $177.91   11.439%   $198.2611   $198.26   $198.25   $198.30  
  7 purchase totals = $913.42       $1,014.7461   $1,014.73   $1,014.70   $1,014.90