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 $243.97   10.491%   $269.5649   $269.56   $269.55   $269.60  
  Purchase #2 $62.78   12.500%   $70.6275   $70.63   $70.65   $70.60  
  Purchase #3 $108.32   10.704%   $119.9146   $119.91   $119.90   $119.90  
  Purchase #4 $161.37   9.116%   $176.0805   $176.08   $176.10   $176.10  
  Purchase #5 $176.31   9.527%   $193.1071   $193.11   $193.10   $193.10  
  Purchase #6 $142.69   6.323%   $151.7123   $151.71   $151.70   $151.70  
  Purchase #7 $68.49   10.714%   $75.828   $75.83   $75.85   $75.80  
  7 purchase totals = $963.93       $1,056.8349   $1,056.83   $1,056.85   $1,056.80