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 $57.42   6.144%   $60.9479   $60.95   $60.95   $60.90  
  Purchase #2 $175.28   11.661%   $195.7194   $195.72   $195.70   $195.70  
  Purchase #3 $148.51   7.341%   $159.4121   $159.41   $159.40   $159.40  
  Purchase #4 $219.67   6.144%   $233.1665   $233.17   $233.15   $233.20  
  Purchase #5 $32.35   7.263%   $34.6996   $34.70   $34.70   $34.70  
  Purchase #6 $143.59   10.363%   $158.4702   $158.47   $158.45   $158.50  
  Purchase #7 $179.40   5.301%   $188.91   $188.91   $188.90   $188.90  
  7 purchase totals = $956.22       $1,031.3257   $1,031.33   $1,031.25   $1,031.30