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 $60.27   12.482%   $67.7929   $67.79   $67.80   $67.80  
  Purchase #2 $25.36   3.493%   $26.2458   $26.25   $26.25   $26.20  
  Purchase #3 $208.28   5.284%   $219.2855   $219.29   $219.30   $219.30  
  Purchase #4 $111.29   11.494%   $124.0817   $124.08   $124.10   $124.10  
  Purchase #5 $210.73   12.597%   $237.2757   $237.28   $237.30   $237.30  
  Purchase #6 $81.92   13.515%   $92.9915   $92.99   $93.00   $93.00  
  Purchase #7 $78.29   3.819%   $81.2799   $81.28   $81.30   $81.30  
  7 purchase totals = $776.14       $848.9530   $848.96   $849.05   $849.00