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 $216.32   13.163%   $244.7942   $244.79   $244.80   $244.80  
  Purchase #2 $182.75   4.482%   $190.9409   $190.94   $190.95   $190.90  
  Purchase #3 $72.29   10.642%   $79.9831   $79.98   $80.00   $80.00  
  Purchase #4 $60.28   3.692%   $62.5055   $62.51   $62.50   $62.50  
  Purchase #5 $242.96   7.299%   $260.6937   $260.69   $260.70   $260.70  
  Purchase #6 $174.49   13.771%   $198.519   $198.52   $198.50   $198.50  
  Purchase #7 $109.88   5.608%   $116.0421   $116.04   $116.05   $116.00  
  7 purchase totals = $1,058.97       $1,153.4785   $1,153.47   $1,153.50   $1,153.40