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 $228.81   6.198%   $242.9916   $242.99   $243.00   $243.00  
  Purchase #2 $229.65   12.159%   $257.5731   $257.57   $257.55   $257.60  
  Purchase #3 $237.48   8.372%   $257.3618   $257.36   $257.35   $257.40  
  Purchase #4 $54.68   8.379%   $59.2616   $59.26   $59.25   $59.30  
  Purchase #5 $26.59   6.803%   $28.3989   $28.40   $28.40   $28.40  
  Purchase #6 $44.33   7.579%   $47.6898   $47.69   $47.70   $47.70  
  Purchase #7 $108.52   5.399%   $114.379   $114.38   $114.40   $114.40  
  7 purchase totals = $930.06       $1,007.6558   $1,007.65   $1,007.65   $1,007.80