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 $37.25   4.472%   $38.9158   $38.92   $38.90   $38.90  
  Purchase #2 $154.49   9.306%   $168.8668   $168.87   $168.85   $168.90  
  Purchase #3 $39.57   10.568%   $43.7518   $43.75   $43.75   $43.80  
  Purchase #4 $203.40   8.551%   $220.7927   $220.79   $220.80   $220.80  
  Purchase #5 $61.84   12.458%   $69.544   $69.54   $69.55   $69.50  
  Purchase #6 $28.83   8.590%   $31.3065   $31.31   $31.30   $31.30  
  Purchase #7 $96.90   9.699%   $106.2983   $106.30   $106.30   $106.30  
  7 purchase totals = $622.28       $679.4759   $679.48   $679.45   $679.50