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 $24.94   5.376%   $26.2808   $26.28   $26.30   $26.30  
  Purchase #2 $49.25   8.122%   $53.2501   $53.25   $53.25   $53.30  
  Purchase #3 $74.47   11.508%   $83.04   $83.04   $83.05   $83.00  
  Purchase #4 $235.81   9.582%   $258.4053   $258.41   $258.40   $258.40  
  Purchase #5 $204.92   10.520%   $226.4776   $226.48   $226.50   $226.50  
  Purchase #6 $15.65   3.853%   $16.253   $16.25   $16.25   $16.30  
  Purchase #7 $227.53   11.110%   $252.8086   $252.81   $252.80   $252.80  
  7 purchase totals = $832.57       $916.5154   $916.52   $916.55   $916.60