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 $51.91   9.383%   $56.7807   $56.78   $56.80   $56.80  
  Purchase #2 $180.86   3.424%   $187.0526   $187.05   $187.05   $187.10  
  Purchase #3 $103.82   5.254%   $109.2747   $109.27   $109.25   $109.30  
  Purchase #4 $54.25   7.248%   $58.182   $58.18   $58.20   $58.20  
  Purchase #5 $249.73   6.867%   $266.879   $266.88   $266.90   $266.90  
  Purchase #6 $230.73   6.260%   $245.1737   $245.17   $245.15   $245.20  
  Purchase #7 $121.56   7.656%   $130.8666   $130.87   $130.85   $130.90  
  7 purchase totals = $992.86       $1,054.2093   $1,054.20   $1,054.20   $1,054.40