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 $246.53   7.705%   $265.5251   $265.53   $265.55   $265.50  
  Purchase #2 $154.71   5.702%   $163.5316   $163.53   $163.55   $163.50  
  Purchase #3 $148.87   3.167%   $153.5847   $153.58   $153.60   $153.60  
  Purchase #4 $172.62   7.705%   $185.9204   $185.92   $185.90   $185.90  
  Purchase #5 $46.71   12.522%   $52.559   $52.56   $52.55   $52.60  
  Purchase #6 $63.68   7.561%   $68.4948   $68.49   $68.50   $68.50  
  Purchase #7 $218.58   3.364%   $225.933   $225.93   $225.95   $225.90  
  7 purchase totals = $1,051.70       $1,115.5486   $1,115.54   $1,115.60   $1,115.50