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 $92.68   12.829%   $104.5699   $104.57   $104.55   $104.60  
  Purchase #2 $81.51   7.589%   $87.6958   $87.70   $87.70   $87.70  
  Purchase #3 $44.49   4.697%   $46.5797   $46.58   $46.60   $46.60  
  Purchase #4 $242.63   11.128%   $269.6299   $269.63   $269.65   $269.60  
  Purchase #5 $188.94   4.864%   $198.13   $198.13   $198.15   $198.10  
  Purchase #6 $157.32   9.351%   $172.031   $172.03   $172.05   $172.00  
  Purchase #7 $165.35   8.551%   $179.4891   $179.49   $179.50   $179.50  
  7 purchase totals = $972.92       $1,058.1254   $1,058.13   $1,058.20   $1,058.10