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 $32.26   12.378%   $36.2531   $36.25   $36.25   $36.30  
  Purchase #2 $144.74   8.609%   $157.2007   $157.20   $157.20   $157.20  
  Purchase #3 $150.45   3.822%   $156.2002   $156.20   $156.20   $156.20  
  Purchase #4 $166.47   11.504%   $185.6207   $185.62   $185.60   $185.60  
  Purchase #5 $178.49   12.861%   $201.4456   $201.45   $201.45   $201.40  
  Purchase #6 $192.93   8.309%   $208.9606   $208.96   $208.95   $209.00  
  Purchase #7 $129.31   4.319%   $134.8949   $134.89   $134.90   $134.90  
  7 purchase totals = $994.65       $1,080.5758   $1,080.57   $1,080.55   $1,080.60