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 $92.93   4.578%   $97.1843   $97.18   $97.20   $97.20  
  Purchase #2 $157.95   13.483%   $179.2464   $179.25   $179.25   $179.20  
  Purchase #3 $10.77   9.621%   $11.8062   $11.81   $11.80   $11.80  
  Purchase #4 $168.68   6.124%   $179.01   $179.01   $179.00   $179.00  
  Purchase #5 $160.91   11.845%   $179.9698   $179.97   $179.95   $180.00  
  Purchase #6 $240.64   11.781%   $268.9898   $268.99   $269.00   $269.00  
  Purchase #7 $128.67   10.376%   $142.0208   $142.02   $142.00   $142.00  
  7 purchase totals = $960.55       $1,058.2273   $1,058.23   $1,058.20   $1,058.20