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 $65.43   12.827%   $73.8227   $73.82   $73.80   $73.80  
  Purchase #2 $172.91   8.364%   $187.3722   $187.37   $187.35   $187.40  
  Purchase #3 $39.72   10.410%   $43.8549   $43.85   $43.85   $43.90  
  Purchase #4 $66.30   11.728%   $74.0757   $74.08   $74.10   $74.10  
  Purchase #5 $226.25   10.191%   $249.3071   $249.31   $249.30   $249.30  
  Purchase #6 $245.91   6.478%   $261.84   $261.84   $261.85   $261.80  
  Purchase #7 $68.27   9.527%   $74.7741   $74.77   $74.75   $74.80  
  7 purchase totals = $884.79       $965.0467   $965.04   $965.00   $965.10