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 $204.70   9.709%   $224.5743   $224.57   $224.55   $224.60  
  Purchase #2 $208.65   8.673%   $226.7462   $226.75   $226.75   $226.70  
  Purchase #3 $166.36   11.194%   $184.9823   $184.98   $185.00   $185.00  
  Purchase #4 $187.88   9.577%   $205.8733   $205.87   $205.85   $205.90  
  Purchase #5 $223.71   5.685%   $236.4279   $236.43   $236.45   $236.40  
  Purchase #6 $191.36   5.331%   $201.5614   $201.56   $201.55   $201.60  
  Purchase #7 $110.70   3.592%   $114.6763   $114.68   $114.70   $114.70  
  7 purchase totals = $1,293.36       $1,394.8417   $1,394.84   $1,394.85   $1,394.90