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 $148.61   11.480%   $165.6704   $165.67   $165.65   $165.70  
  Purchase #2 $31.59   13.338%   $35.8035   $35.80   $35.80   $35.80  
  Purchase #3 $222.43   11.681%   $248.412   $248.41   $248.40   $248.40  
  Purchase #4 $24.31   6.162%   $25.808   $25.81   $25.80   $25.80  
  Purchase #5 $244.74   8.691%   $266.0104   $266.01   $266.00   $266.00  
  Purchase #6 $32.32   13.247%   $36.6014   $36.60   $36.60   $36.60  
  Purchase #7 $171.51   9.263%   $187.397   $187.40   $187.40   $187.40  
  7 purchase totals = $875.51       $965.7027   $965.70   $965.65   $965.70