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 $121.65   3.288%   $125.6499   $125.65   $125.65   $125.60  
  Purchase #2 $218.29   8.569%   $236.9953   $237.00   $237.00   $237.00  
  Purchase #3 $223.66   10.118%   $246.2899   $246.29   $246.30   $246.30  
  Purchase #4 $122.78   5.859%   $129.9737   $129.97   $129.95   $130.00  
  Purchase #5 $93.84   12.170%   $105.2603   $105.26   $105.25   $105.30  
  Purchase #6 $167.50   13.677%   $190.409   $190.41   $190.40   $190.40  
  Purchase #7 $25.97   8.819%   $28.2603   $28.26   $28.25   $28.30  
  7 purchase totals = $973.69       $1,062.8384   $1,062.84   $1,062.80   $1,062.90