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 $56.92   6.721%   $60.7456   $60.75   $60.75   $60.70  
  Purchase #2 $171.34   8.343%   $185.6349   $185.63   $185.65   $185.60  
  Purchase #3 $202.55   13.513%   $229.9206   $229.92   $229.90   $229.90  
  Purchase #4 $210.48   12.843%   $237.5119   $237.51   $237.50   $237.50  
  Purchase #5 $180.42   3.291%   $186.3576   $186.36   $186.35   $186.40  
  Purchase #6 $133.75   10.361%   $147.6078   $147.61   $147.60   $147.60  
  Purchase #7 $55.50   9.564%   $60.808   $60.81   $60.80   $60.80  
  7 purchase totals = $1,010.96       $1,108.5864   $1,108.59   $1,108.55   $1,108.50