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 $168.68   8.749%   $183.4378   $183.44   $183.45   $183.40  
  Purchase #2 $9.83   13.127%   $11.1204   $11.12   $11.10   $11.10  
  Purchase #3 $202.89   7.111%   $217.3175   $217.32   $217.30   $217.30  
  Purchase #4 $168.93   6.835%   $180.4764   $180.48   $180.50   $180.50  
  Purchase #5 $185.72   4.454%   $193.992   $193.99   $194.00   $194.00  
  Purchase #6 $77.27   4.684%   $80.8893   $80.89   $80.90   $80.90  
  Purchase #7 $86.94   6.788%   $92.8415   $92.84   $92.85   $92.80  
  7 purchase totals = $900.26       $960.0749   $960.08   $960.10   $960.00