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 $33.29   6.530%   $35.4638   $35.46   $35.45   $35.50  
  Purchase #2 $149.41   4.788%   $156.5638   $156.56   $156.55   $156.60  
  Purchase #3 $91.41   4.312%   $95.3516   $95.35   $95.35   $95.40  
  Purchase #4 $80.58   12.617%   $90.7468   $90.75   $90.75   $90.70  
  Purchase #5 $237.56   6.330%   $252.5975   $252.60   $252.60   $252.60  
  Purchase #6 $139.68   5.230%   $146.9853   $146.99   $147.00   $147.00  
  Purchase #7 $47.32   7.405%   $50.824   $50.82   $50.80   $50.80  
  7 purchase totals = $779.25       $828.5328   $828.53   $828.50   $828.60