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 $52.47   10.526%   $57.993   $57.99   $58.00   $58.00  
  Purchase #2 $149.47   7.694%   $160.9702   $160.97   $160.95   $161.00  
  Purchase #3 $57.69   8.795%   $62.7638   $62.76   $62.75   $62.80  
  Purchase #4 $110.34   8.236%   $119.4276   $119.43   $119.45   $119.40  
  Purchase #5 $225.25   11.291%   $250.683   $250.68   $250.70   $250.70  
  Purchase #6 $147.37   6.175%   $156.4701   $156.47   $156.45   $156.50  
  Purchase #7 $37.40   7.537%   $40.2188   $40.22   $40.20   $40.20  
  7 purchase totals = $779.99       $848.5265   $848.52   $848.50   $848.60