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 $54.97   5.548%   $58.0197   $58.02   $58.00   $58.00  
  Purchase #2 $192.43   4.671%   $201.4184   $201.42   $201.40   $201.40  
  Purchase #3 $225.98   7.725%   $243.437   $243.44   $243.45   $243.40  
  Purchase #4 $178.67   10.288%   $197.0516   $197.05   $197.05   $197.10  
  Purchase #5 $232.81   4.839%   $244.0757   $244.08   $244.10   $244.10  
  Purchase #6 $125.30   7.394%   $134.5647   $134.56   $134.55   $134.60  
  Purchase #7 $115.37   10.825%   $127.8588   $127.86   $127.85   $127.90  
  7 purchase totals = $1,125.53       $1,206.4259   $1,206.43   $1,206.40   $1,206.50