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 $175.46   5.869%   $185.7577   $185.76   $185.75   $185.80  
  Purchase #2 $234.48   12.655%   $264.1534   $264.15   $264.15   $264.20  
  Purchase #3 $150.55   9.112%   $164.2681   $164.27   $164.25   $164.30  
  Purchase #4 $193.87   6.649%   $206.7604   $206.76   $206.75   $206.80  
  Purchase #5 $206.93   11.426%   $230.5738   $230.57   $230.55   $230.60  
  Purchase #6 $232.51   10.631%   $257.2281   $257.23   $257.25   $257.20  
  Purchase #7 $25.51   8.711%   $27.7322   $27.73   $27.75   $27.70  
  7 purchase totals = $1,219.31       $1,336.4737   $1,336.47   $1,336.45   $1,336.60