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 $114.65   7.320%   $123.0424   $123.04   $123.05   $123.00  
  Purchase #2 $32.89   8.227%   $35.5959   $35.60   $35.60   $35.60  
  Purchase #3 $121.99   10.194%   $134.4257   $134.43   $134.45   $134.40  
  Purchase #4 $89.58   7.354%   $96.1677   $96.17   $96.15   $96.20  
  Purchase #5 $96.41   4.774%   $101.0126   $101.01   $101.00   $101.00  
  Purchase #6 $187.84   13.347%   $212.911   $212.91   $212.90   $212.90  
  Purchase #7 $116.25   11.292%   $129.377   $129.38   $129.40   $129.40  
  7 purchase totals = $759.61       $832.5323   $832.54   $832.55   $832.50