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 $60.34   13.663%   $68.5843   $68.58   $68.60   $68.60  
  Purchase #2 $241.98   4.311%   $252.4118   $252.41   $252.40   $252.40  
  Purchase #3 $28.97   5.156%   $30.4637   $30.46   $30.45   $30.50  
  Purchase #4 $75.39   7.625%   $81.1385   $81.14   $81.15   $81.10  
  Purchase #5 $189.35   5.792%   $200.3172   $200.32   $200.30   $200.30  
  Purchase #6 $222.56   10.668%   $246.3027   $246.30   $246.30   $246.30  
  Purchase #7 $135.76   11.677%   $151.6127   $151.61   $151.60   $151.60  
  7 purchase totals = $954.35       $1,030.8309   $1,030.82   $1,030.80   $1,030.80