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 $155.66   3.613%   $161.284   $161.28   $161.30   $161.30  
  Purchase #2 $180.35   5.148%   $189.6344   $189.63   $189.65   $189.60  
  Purchase #3 $214.93   3.136%   $221.6702   $221.67   $221.65   $221.70  
  Purchase #4 $115.46   6.127%   $122.5342   $122.53   $122.55   $122.50  
  Purchase #5 $11.65   8.672%   $12.6603   $12.66   $12.65   $12.70  
  Purchase #6 $189.57   6.794%   $202.4494   $202.45   $202.45   $202.40  
  Purchase #7 $81.43   4.871%   $85.3965   $85.40   $85.40   $85.40  
  7 purchase totals = $949.05       $995.6290   $995.62   $995.65   $995.60