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 $200.63   4.139%   $208.9341   $208.93   $208.95   $208.90  
  Purchase #2 $173.33   9.242%   $189.3492   $189.35   $189.35   $189.30  
  Purchase #3 $92.44   13.524%   $104.9416   $104.94   $104.95   $104.90  
  Purchase #4 $22.91   9.572%   $25.1029   $25.10   $25.10   $25.10  
  Purchase #5 $116.57   7.832%   $125.6998   $125.70   $125.70   $125.70  
  Purchase #6 $181.56   11.643%   $202.699   $202.70   $202.70   $202.70  
  Purchase #7 $198.84   10.179%   $219.0799   $219.08   $219.10   $219.10  
  7 purchase totals = $986.28       $1,075.8065   $1,075.80   $1,075.85   $1,075.70