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 $164.29   12.582%   $184.961   $184.96   $184.95   $185.00  
  Purchase #2 $235.81   8.391%   $255.5968   $255.60   $255.60   $255.60  
  Purchase #3 $41.83   7.571%   $44.9969   $45.00   $45.00   $45.00  
  Purchase #4 $206.49   6.834%   $220.6015   $220.60   $220.60   $220.60  
  Purchase #5 $113.64   4.667%   $118.9436   $118.94   $118.95   $118.90  
  Purchase #6 $15.27   5.113%   $16.0508   $16.05   $16.05   $16.10  
  Purchase #7 $66.41   5.818%   $70.2737   $70.27   $70.25   $70.30  
  7 purchase totals = $843.74       $911.4243   $911.42   $911.40   $911.50