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 $88.63   8.617%   $96.2672   $96.27   $96.25   $96.30  
  Purchase #2 $43.30   4.430%   $45.2182   $45.22   $45.20   $45.20  
  Purchase #3 $194.31   11.331%   $216.3273   $216.33   $216.35   $216.30  
  Purchase #4 $154.81   4.435%   $161.6758   $161.68   $161.70   $161.70  
  Purchase #5 $239.93   3.119%   $247.4134   $247.41   $247.40   $247.40  
  Purchase #6 $223.29   5.498%   $235.5665   $235.57   $235.55   $235.60  
  Purchase #7 $24.81   7.553%   $26.6839   $26.68   $26.70   $26.70  
  7 purchase totals = $969.08       $1,029.1523   $1,029.16   $1,029.15   $1,029.20