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 $34.64   8.657%   $37.6388   $37.64   $37.65   $37.60  
  Purchase #2 $218.26   13.718%   $248.2009   $248.20   $248.20   $248.20  
  Purchase #3 $55.66   13.705%   $63.2882   $63.29   $63.30   $63.30  
  Purchase #4 $203.31   6.811%   $217.1574   $217.16   $217.15   $217.20  
  Purchase #5 $24.99   13.305%   $28.3149   $28.31   $28.30   $28.30  
  Purchase #6 $145.39   5.303%   $153.1   $153.10   $153.10   $153.10  
  Purchase #7 $102.61   13.341%   $116.2992   $116.30   $116.30   $116.30  
  7 purchase totals = $784.86       $863.9994   $864.00   $864.00   $864.00