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 $57.90   8.167%   $62.6287   $62.63   $62.65   $62.60  
  Purchase #2 $138.32   5.156%   $145.4518   $145.45   $145.45   $145.50  
  Purchase #3 $243.50   3.587%   $252.2343   $252.23   $252.25   $252.20  
  Purchase #4 $160.58   8.856%   $174.801   $174.80   $174.80   $174.80  
  Purchase #5 $179.70   3.256%   $185.551   $185.55   $185.55   $185.60  
  Purchase #6 $246.48   7.677%   $265.4023   $265.40   $265.40   $265.40  
  Purchase #7 $197.79   7.873%   $213.362   $213.36   $213.35   $213.40  
  7 purchase totals = $1,224.27       $1,299.4311   $1,299.42   $1,299.45   $1,299.50