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 $61.85   13.662%   $70.2999   $70.30   $70.30   $70.30  
  Purchase #2 $109.99   6.450%   $117.0844   $117.08   $117.10   $117.10  
  Purchase #3 $190.65   7.423%   $204.8019   $204.80   $204.80   $204.80  
  Purchase #4 $158.80   5.773%   $167.9675   $167.97   $167.95   $168.00  
  Purchase #5 $222.38   10.633%   $246.0257   $246.03   $246.05   $246.00  
  Purchase #6 $52.80   6.506%   $56.2352   $56.24   $56.25   $56.20  
  Purchase #7 $221.87   10.282%   $244.6827   $244.68   $244.70   $244.70  
  7 purchase totals = $1,018.34       $1,107.0973   $1,107.10   $1,107.15   $1,107.10