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 $56.58   8.395%   $61.3299   $61.33   $61.35   $61.30  
  Purchase #2 $104.91   9.469%   $114.8439   $114.84   $114.85   $114.80  
  Purchase #3 $45.42   4.465%   $47.448   $47.45   $47.45   $47.40  
  Purchase #4 $154.35   7.165%   $165.4092   $165.41   $165.40   $165.40  
  Purchase #5 $217.25   6.165%   $230.6435   $230.64   $230.65   $230.60  
  Purchase #6 $224.47   3.698%   $232.7709   $232.77   $232.75   $232.80  
  Purchase #7 $199.71   3.647%   $206.9934   $206.99   $207.00   $207.00  
  7 purchase totals = $1,002.69       $1,059.4388   $1,059.43   $1,059.45   $1,059.30