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 $7.50   5.459%   $7.9094   $7.91   $7.90   $7.90  
  Purchase #2 $169.72   6.470%   $180.7009   $180.70   $180.70   $180.70  
  Purchase #3 $144.91   6.285%   $154.0176   $154.02   $154.00   $154.00  
  Purchase #4 $233.85   9.169%   $255.2917   $255.29   $255.30   $255.30  
  Purchase #5 $117.25   10.200%   $129.2095   $129.21   $129.20   $129.20  
  Purchase #6 $248.44   10.538%   $274.6206   $274.62   $274.60   $274.60  
  Purchase #7 $72.81   4.841%   $76.3347   $76.33   $76.35   $76.30  
  7 purchase totals = $994.48       $1,078.0844   $1,078.08   $1,078.05   $1,078.00