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 $227.29   13.529%   $258.0401   $258.04   $258.05   $258.00  
  Purchase #2 $88.76   8.486%   $96.2922   $96.29   $96.30   $96.30  
  Purchase #3 $209.33   8.224%   $226.5453   $226.55   $226.55   $226.50  
  Purchase #4 $14.95   10.118%   $16.4626   $16.46   $16.45   $16.50  
  Purchase #5 $201.61   10.820%   $223.4242   $223.42   $223.40   $223.40  
  Purchase #6 $180.96   6.836%   $193.3304   $193.33   $193.35   $193.30  
  Purchase #7 $152.45   7.239%   $163.4859   $163.49   $163.50   $163.50  
  7 purchase totals = $1,075.35       $1,177.5807   $1,177.58   $1,177.60   $1,177.50