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 $203.41   6.210%   $216.0418   $216.04   $216.05   $216.00  
  Purchase #2 $226.51   9.741%   $248.5743   $248.57   $248.55   $248.60  
  Purchase #3 $90.47   9.186%   $98.7806   $98.78   $98.80   $98.80  
  Purchase #4 $248.27   7.748%   $267.506   $267.51   $267.50   $267.50  
  Purchase #5 $238.45   8.227%   $258.0673   $258.07   $258.05   $258.10  
  Purchase #6 $109.67   6.220%   $116.4915   $116.49   $116.50   $116.50  
  Purchase #7 $163.37   4.656%   $170.9765   $170.98   $171.00   $171.00  
  7 purchase totals = $1,280.15       $1,376.4380   $1,376.44   $1,376.45   $1,376.50