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 $214.66   12.379%   $241.2328   $241.23   $241.25   $241.20  
  Purchase #2 $40.35   10.456%   $44.569   $44.57   $44.55   $44.60  
  Purchase #3 $25.96   6.461%   $27.6373   $27.64   $27.65   $27.60  
  Purchase #4 $200.48   5.268%   $211.0413   $211.04   $211.05   $211.00  
  Purchase #5 $23.50   8.861%   $25.5823   $25.58   $25.60   $25.60  
  Purchase #6 $207.80   13.308%   $235.454   $235.45   $235.45   $235.50  
  Purchase #7 $163.69   10.119%   $180.2538   $180.25   $180.25   $180.30  
  7 purchase totals = $876.44       $965.7705   $965.76   $965.80   $965.80