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 $246.57   6.270%   $262.0299   $262.03   $262.05   $262.00  
  Purchase #2 $133.89   4.325%   $139.6807   $139.68   $139.70   $139.70  
  Purchase #3 $136.39   12.396%   $153.2969   $153.30   $153.30   $153.30  
  Purchase #4 $34.84   8.624%   $37.8446   $37.84   $37.85   $37.80  
  Purchase #5 $150.78   13.738%   $171.4942   $171.49   $171.50   $171.50  
  Purchase #6 $15.26   8.140%   $16.5022   $16.50   $16.50   $16.50  
  Purchase #7 $102.41   13.735%   $116.476   $116.48   $116.50   $116.50  
  7 purchase totals = $820.14       $897.3245   $897.32   $897.40   $897.30