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 $242.64   10.656%   $268.4957   $268.50   $268.50   $268.50  
  Purchase #2 $53.69   3.569%   $55.6062   $55.61   $55.60   $55.60  
  Purchase #3 $156.49   11.211%   $174.0341   $174.03   $174.05   $174.00  
  Purchase #4 $10.30   11.173%   $11.4508   $11.45   $11.45   $11.50  
  Purchase #5 $200.50   4.703%   $209.9295   $209.93   $209.95   $209.90  
  Purchase #6 $238.75   8.453%   $258.9315   $258.93   $258.95   $258.90  
  Purchase #7 $70.62   13.123%   $79.8875   $79.89   $79.90   $79.90  
  7 purchase totals = $972.99       $1,058.3353   $1,058.34   $1,058.40   $1,058.30