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 $92.27   13.448%   $104.6785   $104.68   $104.70   $104.70  
  Purchase #2 $89.57   4.587%   $93.6786   $93.68   $93.70   $93.70  
  Purchase #3 $139.95   11.803%   $156.4683   $156.47   $156.45   $156.50  
  Purchase #4 $212.34   6.419%   $225.9701   $225.97   $225.95   $226.00  
  Purchase #5 $233.58   13.848%   $265.9262   $265.93   $265.95   $265.90  
  Purchase #6 $97.53   12.671%   $109.888   $109.89   $109.90   $109.90  
  Purchase #7 $57.37   12.615%   $64.6072   $64.61   $64.60   $64.60  
  7 purchase totals = $922.61       $1,021.2169   $1,021.23   $1,021.25   $1,021.30