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 $227.82   11.624%   $254.3018   $254.30   $254.30   $254.30  
  Purchase #2 $68.29   12.530%   $76.8467   $76.85   $76.85   $76.80  
  Purchase #3 $189.61   12.167%   $212.6798   $212.68   $212.70   $212.70  
  Purchase #4 $23.25   7.576%   $25.0114   $25.01   $25.00   $25.00  
  Purchase #5 $166.75   9.509%   $182.6063   $182.61   $182.60   $182.60  
  Purchase #6 $124.52   8.221%   $134.7568   $134.76   $134.75   $134.80  
  Purchase #7 $179.54   3.766%   $186.3015   $186.30   $186.30   $186.30  
  7 purchase totals = $979.78       $1,072.5043   $1,072.51   $1,072.50   $1,072.50