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 $247.57   8.661%   $269.012   $269.01   $269.00   $269.00  
  Purchase #2 $58.72   9.631%   $64.3753   $64.38   $64.40   $64.40  
  Purchase #3 $212.78   11.684%   $237.6412   $237.64   $237.65   $237.60  
  Purchase #4 $77.58   3.866%   $80.5792   $80.58   $80.60   $80.60  
  Purchase #5 $115.57   11.823%   $129.2338   $129.23   $129.25   $129.20  
  Purchase #6 $248.42   7.137%   $266.1497   $266.15   $266.15   $266.10  
  Purchase #7 $12.39   3.487%   $12.822   $12.82   $12.80   $12.80  
  7 purchase totals = $973.03       $1,059.8132   $1,059.81   $1,059.85   $1,059.70