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 $39.78   9.402%   $43.5201   $43.52   $43.50   $43.50  
  Purchase #2 $235.86   10.391%   $260.3682   $260.37   $260.35   $260.40  
  Purchase #3 $245.34   9.555%   $268.7822   $268.78   $268.80   $268.80  
  Purchase #4 $53.76   4.239%   $56.0389   $56.04   $56.05   $56.00  
  Purchase #5 $65.48   6.812%   $69.9405   $69.94   $69.95   $69.90  
  Purchase #6 $118.95   8.491%   $129.05   $129.05   $129.05   $129.10  
  Purchase #7 $177.76   11.639%   $198.4495   $198.45   $198.45   $198.40  
  7 purchase totals = $936.93       $1,026.1494   $1,026.15   $1,026.15   $1,026.10