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 $54.28   9.547%   $59.4621   $59.46   $59.45   $59.50  
  Purchase #2 $161.54   8.539%   $175.3339   $175.33   $175.35   $175.30  
  Purchase #3 $148.64   13.165%   $168.2085   $168.21   $168.20   $168.20  
  Purchase #4 $247.59   5.431%   $261.0366   $261.04   $261.05   $261.00  
  Purchase #5 $245.49   9.683%   $269.2608   $269.26   $269.25   $269.30  
  Purchase #6 $134.89   4.311%   $140.7051   $140.71   $140.70   $140.70  
  Purchase #7 $145.67   13.471%   $165.2932   $165.29   $165.30   $165.30  
  7 purchase totals = $1,138.10       $1,239.3002   $1,239.30   $1,239.30   $1,239.30