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 $113.71   11.631%   $126.9356   $126.94   $126.95   $126.90  
  Purchase #2 $12.75   11.294%   $14.19   $14.19   $14.20   $14.20  
  Purchase #3 $29.62   3.465%   $30.6463   $30.65   $30.65   $30.60  
  Purchase #4 $48.81   5.516%   $51.5024   $51.50   $51.50   $51.50  
  Purchase #5 $63.61   11.654%   $71.0231   $71.02   $71.00   $71.00  
  Purchase #6 $30.46   10.388%   $33.6242   $33.62   $33.60   $33.60  
  Purchase #7 $61.49   10.854%   $68.1641   $68.16   $68.15   $68.20  
  7 purchase totals = $360.45       $396.0857   $396.08   $396.05   $396.00