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 $196.68   4.183%   $204.9071   $204.91   $204.90   $204.90  
  Purchase #2 $181.86   10.561%   $201.0662   $201.07   $201.05   $201.10  
  Purchase #3 $49.62   12.409%   $55.7773   $55.78   $55.80   $55.80  
  Purchase #4 $25.62   3.861%   $26.6092   $26.61   $26.60   $26.60  
  Purchase #5 $67.66   8.850%   $73.6479   $73.65   $73.65   $73.60  
  Purchase #6 $47.36   5.599%   $50.0117   $50.01   $50.00   $50.00  
  Purchase #7 $248.68   6.670%   $265.267   $265.27   $265.25   $265.30  
  7 purchase totals = $817.48       $877.2864   $877.30   $877.25   $877.30