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 $55.50   11.258%   $61.7482   $61.75   $61.75   $61.70  
  Purchase #2 $24.56   8.361%   $26.6135   $26.61   $26.60   $26.60  
  Purchase #3 $153.55   13.371%   $174.0812   $174.08   $174.10   $174.10  
  Purchase #4 $237.68   9.191%   $259.5252   $259.53   $259.55   $259.50  
  Purchase #5 $185.58   9.239%   $202.7257   $202.73   $202.75   $202.70  
  Purchase #6 $128.50   8.450%   $139.3583   $139.36   $139.35   $139.40  
  Purchase #7 $33.25   7.191%   $35.641   $35.64   $35.65   $35.60  
  7 purchase totals = $818.62       $899.6931   $899.70   $899.75   $899.60