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 $61.29   9.741%   $67.2603   $67.26   $67.25   $67.30  
  Purchase #2 $85.58   12.692%   $96.4418   $96.44   $96.45   $96.40  
  Purchase #3 $204.36   9.701%   $224.185   $224.19   $224.20   $224.20  
  Purchase #4 $230.66   8.678%   $250.6767   $250.68   $250.70   $250.70  
  Purchase #5 $52.92   13.528%   $60.079   $60.08   $60.10   $60.10  
  Purchase #6 $63.50   6.822%   $67.832   $67.83   $67.85   $67.80  
  Purchase #7 $191.45   3.420%   $197.9976   $198.00   $198.00   $198.00  
  7 purchase totals = $889.76       $964.4724   $964.48   $964.55   $964.50