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 $63.25   8.398%   $68.5617   $68.56   $68.55   $68.60  
  Purchase #2 $186.54   11.255%   $207.5351   $207.54   $207.55   $207.50  
  Purchase #3 $162.60   6.457%   $173.0991   $173.10   $173.10   $173.10  
  Purchase #4 $67.96   5.783%   $71.8901   $71.89   $71.90   $71.90  
  Purchase #5 $64.83   7.133%   $69.4543   $69.45   $69.45   $69.50  
  Purchase #6 $65.91   8.730%   $71.6639   $71.66   $71.65   $71.70  
  Purchase #7 $220.35   11.675%   $246.0759   $246.08   $246.10   $246.10  
  7 purchase totals = $831.44       $908.2801   $908.28   $908.30   $908.40