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 $23.45   9.602%   $25.7017   $25.70   $25.70   $25.70  
  Purchase #2 $166.68   9.592%   $182.6679   $182.67   $182.65   $182.70  
  Purchase #3 $153.69   13.340%   $174.1922   $174.19   $174.20   $174.20  
  Purchase #4 $186.71   9.121%   $203.7398   $203.74   $203.75   $203.70  
  Purchase #5 $201.77   3.447%   $208.725   $208.73   $208.75   $208.70  
  Purchase #6 $81.28   10.136%   $89.5185   $89.52   $89.50   $89.50  
  Purchase #7 $177.62   5.580%   $187.5312   $187.53   $187.55   $187.50  
  7 purchase totals = $991.20       $1,072.0763   $1,072.08   $1,072.10   $1,072.00