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 $214.25   5.788%   $226.6508   $226.65   $226.65   $226.70  
  Purchase #2 $191.92   3.497%   $198.6314   $198.63   $198.65   $198.60  
  Purchase #3 $80.68   5.859%   $85.407   $85.41   $85.40   $85.40  
  Purchase #4 $120.94   13.517%   $137.2875   $137.29   $137.30   $137.30  
  Purchase #5 $239.42   3.312%   $247.3496   $247.35   $247.35   $247.30  
  Purchase #6 $189.57   10.800%   $210.0436   $210.04   $210.05   $210.00  
  Purchase #7 $126.52   9.326%   $138.3193   $138.32   $138.30   $138.30  
  7 purchase totals = $1,163.30       $1,243.6892   $1,243.69   $1,243.70   $1,243.60